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/lib/storage.ts

@@ -14,7 +14,7 @@ export const LS = {
   lang: "siftlode.lang",
   filters: "siftlode.filters",
   page: "siftlode.page",
-  // E24: start every session on the Home surface rather than on the module you happened to leave
+  // Start every session on the Home surface rather than on the module you happened to leave
   // open. Per-account, "0" = opt out and go back to remembering the last module. Read by
   // `loadInitialPage` in NavigationProvider's initializer, which BootGate runs only once the tab's
   // account is pinned — so the landing is decided right before the first paint, never corrected after.
@@ -182,7 +182,7 @@ export function useAccountPersistedState(
 
 // Which sub-tab a page was left on (Settings, Configuration, Statistics, Users) is kept for THIS browser
 // tab only — sessionStorage, account-scoped: it survives a reload and a trip to another page, and a new
-// tab opens the page on its first sub-tab (the owner, E31: a position remembered forever in
+// tab opens the page on its first sub-tab (the owner's call: a position remembered forever in
 // localStorage made Configuration open on "Plex" in every fresh tab, as if that were its home).
 
 /** The sub-tab stored for this browser tab, or null. */
@@ -212,7 +212,7 @@ export function useTabPersistedState(
   fallback = "",
 ): [string, (value: string) => void] {
   const [value, setValue] = useState<string>(() => {
-    // Before E31 the position lived in localStorage; a value left there would never be read again.
+    // The position used to live in localStorage; a value left there would never be read again.
     const old = accountKey(base);
     if (old) {
       try {