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/Home.tsx

@@ -73,7 +73,7 @@ import {
   mediaTitleClass,
 } from "./ui/mediaCardStyles";
 
-// The Home surface (E24) — "Mit nézzek most?".
+// The Home surface — "Mit nézzek most?".
 //
 // Layout C+, chosen from mockups: the time-budget chips sit ABOVE a single large hero, so the
 // question comes first and the hero is its answer; the shelves follow, compact. The page's whole
@@ -144,7 +144,7 @@ function useHomeCardMenu({
   // the scroll, and because these rows are keyboard-reachable (Shift+F10) for free.
   const menu = useContextMenu<DiscoverCard>();
   const pin = useComfortPin(menu.open);
-  // A video tile's own action list (E28 C1), the same one the feed's menu shows; the rail keeps its
+  // A video tile's own action list, the same one the feed's menu shows; the rail keeps its
   // Play row (it resolves `next`) and its shelf rows around it.
   const videoActions = useVideoActions({ onState, onToggleSave }, menu.open);
   // A Plex tile's, likewise (its "Media info" row goes where the tile's `onInfo` does).
@@ -723,7 +723,7 @@ export default function Home() {
   }, [budget, seed, press, seen]);
   const [player, setPlayer] = useState<{ video: Video; startAt: number | null } | null>(null);
 
-  // A Plex card's title is in the reader's language (E30), so the answer is cached per language.
+  // A Plex card's title is in the reader's language, so the answer is cached per language.
   const lang = plexLang(i18n.language);
   const q = useQuery({
     queryKey: qk.discover(budget, lang),
@@ -745,7 +745,7 @@ export default function Home() {
     //
     // But only WITHIN a budget. Plain `keepPreviousData` chains through the disabled seed-0 query a
     // chip click leaves behind, so the first reroll under a new budget held up the card the PREVIOUS
-    // question was answered with — under a chip promising something else (round 2). Returning
+    // question was answered with — under a chip promising something else. Returning
     // undefined instead falls the hero back to this budget's own loaded answer, which is already in
     // hand; the spinner still covers the wait.
     placeholderData: (prev) => (prev?.budget === budget ? prev : undefined),
@@ -754,11 +754,11 @@ export default function Home() {
   // `["discover"]` prefix so a mutation's invalidation reaches the rerolled hero — which also means
   // every mark-watched, bookmark, pin/unpin and shelf move on this page refetches it in the
   // background, and `ui/Button` turns `loading` into `disabled`. So the reroll spun and swallowed
-  // clicks after actions the user never associated with it (round 2). A press is outstanding exactly
+  // clicks after actions the user never associated with it. A press is outstanding exactly
   // while THIS key has never settled — which is what `isFetched` means (react-query counts both a
   // success and an error as settled), and every press mints a fresh seed, so a fresh key.
   //
-  // Round 3 corrected this: `isPlaceholderData || data === undefined` looked equivalent and was not.
+  // Since corrected: `isPlaceholderData || data === undefined` looked equivalent and was not.
   // A pick that FAILED leaves its key data-less forever (`retry: false`), so the second disjunct
   // stayed true and the next unrelated mutation re-disabled the button — the same defect, surviving
   // in the error branch. Guarding on `!isError` does NOT help either: query-core resets a data-less
@@ -775,7 +775,7 @@ export default function Home() {
   // reset an answer that already resolved, so an untagged slot outlived the question it answered —
   // switch to "10 perc", press reroll, let that request fail (`retry: false`, so it is terminal),
   // and the two-hour film picked under "Bármennyi" was still the hero, under a chip promising ten
-  // minutes (round 2). Taken from the SERVER's `budget` echo rather than this render's state, so the
+  // minutes. Taken from the SERVER's `budget` echo rather than this render's state, so the
   // tag cannot be minted from a budget the pick never answered.
   const [lastPick, setLastPick] = useState<{
     budget: DiscoverBudget;
@@ -802,7 +802,7 @@ export default function Home() {
           // pick for this budget resolved to no hero" is a real answer, not a missing one. Under
           // `??` the two collapsed, so a failed press after an empty pick resurrected the card the
           // page loaded with — which it had already excluded as seen and just said it had nothing
-          // beyond (round 3). A mismatched or absent tag still falls through to the loaded hero,
+          // beyond. A mismatched or absent tag still falls through to the loaded hero,
           // which is what the FIRST press of a budget needs.
           lastPick?.budget === budget
           ? lastPick.hero