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/compilerCoverage.contract.test.ts

@@ -5,16 +5,16 @@ import { compileReport, shippedSources, type CompileReport } from "./compilerSki
 // still works, it just re-renders everything under it on every render. The channel manager is where
 // it hurt (the owner, 2026-10-03): Channels and DataTable both bailed out, every open, close and
 // reposition of a row's right-click menu rebuilt the rows and columns, and on "All" rows the menu
-// took ~0.9 s to open and ~0.6 s to close. The E32 audit then found 95 such functions across src.
+// took ~0.9 s to open and ~0.6 s to close. An audit then found 95 such functions across src.
 //
-// A RATCHET over everything the build compiles (E32 S1). KNOWN_SKIPS is the exact set the compiler
+// A RATCHET over everything the build compiles. KNOWN_SKIPS is the exact set the compiler
 // skips today, `file → function → the compiler's category`; everything else must compile. Both
 // directions are red:
 //   • a NEW skip (or a known one changing category) — fix the function; if it truly cannot be
 //     compiled, adding it here is a decision for the owner, with the reason in docs/gates.md;
 //   • a skip that is GONE — delete its entry, so the list only ever shrinks.
-// E32 burned it down from 93 to the one function below: S3 read the popover engine through
-// destructuring and moved every render-phase ref write to `useEffectEvent` / `useLatest`; S4 took
+// A cleanup burned it down from 93 to the one function below: it read the popover engine through
+// destructuring, moved every render-phase ref write to `useEffectEvent` / `useLatest`, took
 // try/finally and every conditional, loop or optional call out of try blocks (the compiler cannot
 // lower them yet — and `react-hooks/todo` does not see the latter, so THIS test is what catches them)
 // and replaced the two exhaustive-deps suppressions, each of which skipped its whole function.
@@ -28,11 +28,11 @@ const KNOWN_SKIPS: CompileReport["skipped"] = {
 const MUST_COMPILE: Record<string, string[]> = {
   "components/Channels.tsx": ["Channels"],
   "components/ui/DataTable.tsx": ["DataTable"],
-  // Under every button and every popover in the app (E32 S3).
+  // Under every button and every popover in the app.
   "components/ui/FocusSafeButton.tsx": ["FocusSafeButton"],
   "components/ui/anchoredPopoverHooks.ts": ["useAnchoredPopover"],
   "components/ui/AnchoredPopover.tsx": ["PopoverSurfaceInner"],
-  // The two players — the largest components here, and the last to compile (E32 S4).
+  // The two players — the largest components here, and the last to compile.
   "components/PlexPlayer.tsx": ["PlexPlayer"],
   "components/PlayerModal.tsx": ["PlayerModal"],
   "lib/playerModalHooks.ts": ["useYtProgress"],