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/PlexCollectionView.dom.test.tsx

@@ -1,7 +1,7 @@
 // @vitest-environment jsdom
 //
-// S4 Play-all — buildQueue's show→episode expansion and playAll's decision branch, the honest-states
-// behaviour the deep-review flagged as untested. A leaf member queues as itself; a show member is
+// Play-all — buildQueue's show→episode expansion and playAll's decision branch, the honest-states
+// behaviour a review flagged as untested. A leaf member queues as itself; a show member is
 // expanded (lazily, on click) into its episodes in season→episode order; a show that expands to zero
 // episodes must NOT silently no-op but surface the `playEmpty` info notice. api.plexCollection /
 // api.plexShow are stubbed so the queries resolve synchronously; notify is spied to assert the notice.
@@ -142,7 +142,7 @@ describe("PlexCollectionView — Play-all", () => {
   });
 });
 
-// Bug-hunt deep-review: the Sort control put the sort into the detail query's key, and two things
+// Bug hunt: the Sort control put the sort into the detail query's key, and two things
 // on this page did not follow it.
 describe("PlexCollectionView — after the sort joined the query key", () => {
   it("flips a poster's watched state on the page it was clicked on", async () => {
@@ -212,7 +212,7 @@ describe("PlexCollectionView — after the sort joined the query key", () => {
   });
 });
 
-describe("PlexCollectionView — the reader's language (E30)", () => {
+describe("PlexCollectionView — the reader's language", () => {
   it("asks for the members, and a show it expands, in Hungarian", async () => {
     setLanguage("hu");
     try {
@@ -228,7 +228,7 @@ describe("PlexCollectionView — the reader's language (E30)", () => {
   });
 });
 
-describe("PlexCollectionView — the summary (E30 review)", () => {
+describe("PlexCollectionView — the summary", () => {
   it("offers no More under a summary that fits", async () => {
     vi.spyOn(api, "plexCollection").mockResolvedValue({
       ...detail([card("m1", "movie")]),