chore(comments): drop epic, sprint and review-round ids from the code

The code cited its plan instead of saying why: `E28 review J4`, `(R6 S3b)`, `S1 justified…`,
`deep-review round 5`. That plan lives in the private ops repo, so for every reader of this one the
citation was noise, and a sentence whose subject was the plan step ("round 2 showed…") hid its
lesson behind an id. Each one is gone and the "why" kept: a bare citation is deleted, a sentence
carrying a lesson is reworded around it ("a later attempt showed…").

Measured (`scripts/audit_metrics.py`, product code): 652 lines in 270 files carried an epic code by
the definition the next commit holds (507 / 241 by the old, two-digit-only one) -> 0. Across all
code, tests, scripts and configs: ~1100 epic-code lines plus ~320 sprint/round ids.

Behaviour unchanged, checked mechanically: every changed .py file has the same AST once docstrings
are blanked; css/sh/toml/yml/json files are identical once comments are stripped; the only
non-comment changes in TS/JS are test titles, one description string in a contract table, and five
ESLint messages, whose text is all the gates snapshot diff holds. Not touched: Markdown (docs and
the changelog keep their history), Alembic migrations, TV episode notation (`S2 · E5`), DESIGN.md
ids (`C1`, `B4`, `S3h`), tracker ids (`SEC-16`, `DX-17`).

One stale claim fixed on the way: test_hls_reaper's docstring said the player checkpoints "every
10 s whether or not it is playing", which plex/stream.py calls wrong; it now says what the code does.

frontend/src/components/Channels.tsx

@@ -211,7 +211,7 @@ export default function Channels() {
     onError: () => qc.invalidateQueries({ queryKey: qk.channels() }),
   });
 
-  // A priority step picked from the row's menu (E28 S3e3b, owner): the one thing a pick is FOR is
+  // A priority step picked from the row's menu (the owner's call): the one thing a pick is FOR is
   // to move the channel up (or down) the list, so the list re-sorts at once — only that row moves
   // (`placeByPriority`, the server's order) — and the page and the focus follow it (`follow`): the
   // table/card pager turns to its page, and the effect below hands the focus to its "…" (its node
@@ -248,7 +248,7 @@ export default function Channels() {
       // Keep the channel DETAIL cache in step with the manager list (the detail page reads its tags
       // from qk.channel(id)); mirrors the detail page invalidating the manager list on its side. Also
       // recompute suggestions: a channel that just gained/lost a user tag changes the untagged set and
-      // the learned pattern (E8·S4).
+      // the learned pattern.
       onSuccess: (id) => {
         qc.invalidateQueries({ queryKey: qk.channel(id) });
         qc.invalidateQueries({ queryKey: qk.tagSuggestions() });
@@ -267,7 +267,7 @@ export default function Channels() {
   // The options are a memo so the hook's toggleTag/createAndAttachTag stay the same functions: the
   // column memo below names them (see `columns`).
   const { toggleTag, createAndAttachTag } = useChannelTagActions(tagActionOpts);
-  // --- Suggested tags (E8·S4): learned from the user's own manual-tag pattern, shown as accept/dismiss
+  // --- Suggested tags: learned from the user's own manual-tag pattern, shown as accept/dismiss
   // ghost chips on untagged channels. Dismissal is session-only (an accepted suggestion self-clears —
   // the channel becomes tagged and the server drops it; a dismissed one just hides until reload). The
   // /tags/suggestions query, the session dismiss set, and the optimistic accept/dismiss/bulk logic all
@@ -311,7 +311,7 @@ export default function Channels() {
   // funnel share ONE state and stay in sync (bidirectional). Toggling a chip rewrites `filters.tags`;
   // filterRows / DataTable then applies it. Channel-name search stays separate (the shared top box).
   const tagFilter = Array.isArray(filters.tags) ? filters.tags : [];
-  // B4 (E28 review L7): on a short window the band's filters — the tag chip lane and the status /
+  // B4: on a short window the band's filters — the tag chip lane and the status /
   // pager row — fold behind one "Filters · n"; the tabs and the TAGS editor stay. n = each picked tag,
   // plus every other active column filter (the status chips are the Sync column's).
   const fold = useFilterFold();
@@ -369,7 +369,7 @@ export default function Channels() {
     (c: ManagedChannel) => onViewChannel(c.id, c.title ?? t("channels.row.thisChannel")),
     [onViewChannel, t],
   );
-  // The channel's ONE action list (E28 C1) — ONE menu for the list, shared by the table and the card
+  // The channel's ONE action list — ONE menu for the list, shared by the table and the card
   // layout: they are two paints of the same rows, so a right-click, a long-press and the row's "…"
   // must mean the same thing in both. Only mounted under the SUBSCRIBED branch below: a discovery
   // result is not a `Channel` row yet, so pinning or hiding one could only 404.
@@ -405,7 +405,7 @@ export default function Channels() {
 
   // Tag/priority/text filters stay controlled COLUMN filters (`filters.tags` etc.) shared by the top
   // chips, the column funnels and the cards. The sync-status filter (`filters.sync`) is no longer a
-  // column — R14 retired the Sync column and folded its status into a ✓ charm on Stored — so it's
+  // column — the retired Sync column became a ✓ charm on Stored — so it's
   // applied as a pre-filter (`applySyncFilter`) over the rows fed to BOTH the table and the cards,
   // still driven by the same top chips. Hidden channels have their own tab (excluded here). Only the
   // name search filters at this step; the remaining column funnels run in DataTable / filterRows below.
@@ -698,7 +698,7 @@ export default function Channels() {
             {/* One row: the TAGS editor trigger (left) + the tag-filter chip lane (folds overflow into
           "+N") + Clear, then the catalog "…" actions pinned right, so the "…" menu always stays on the
           first line. Only the suggestions block wraps: below 40rem it takes a line of its own under
-          the row (E28 S3f3, the owner's pick A) — at 375 it had squeezed the chip lane to 0 px and
+          the row (the owner's pick) — at 375 it had squeezed the chip lane to 0 px and
           pushed the "…" off the screen. Channel-name search lives in the shared top SearchBar. */}
             <div className="flex flex-wrap items-center gap-2 min-w-0">
               {/* The "TAGS" label IS the tags-editor trigger (pencil), replacing the separate
@@ -725,7 +725,7 @@ export default function Channels() {
                   {t("datatable.clear")}
                 </Button>
               )}
-              {/* Suggested-tags affordance (E8·S4): a sparkle count of the visible suggestions, with a
+              {/* Suggested-tags affordance: a sparkle count of the visible suggestions, with a
                   one-click bulk-accept for the high-confidence ones. The per-row ghost chips handle the
                   rest. Hidden when there's nothing to suggest. */}
               {visibleSuggestions.length > 0 && (
@@ -865,7 +865,7 @@ export default function Channels() {
                   rowClassName={() => "group"}
                 />
                 {/* Folded, the status / pager row leaves the band, as the table's does — and the
-                    list's own end keeps it here too (round 2, F2: the cards had lost their pager). */}
+                    list's own end keeps it here too (the cards had once lost their pager). */}
                 {fold.folded && (
                   <div className="pt-3 flex items-center justify-between gap-3 flex-wrap">
                     {statusChips}