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/releaseNotes.ts

@@ -1,8 +1,8 @@
 // User-facing release notes: one entry per released version, newest first, as text in
 // content/release-notes/<lang>.json rather than code, so the dialog loads only the UI language's file
 // and only when it opens. A note says what a user notices, under "new" or "fixed", each item a
-// sentence or two; internal work is not listed. Internal work never ships on its own either (owner,
-// E28): it waits for the next release a user can see, so the newest entry always has an item.
+// sentence or two; internal work is not listed. Internal work never ships on its own either (owner
+// decision): it waits for the next release a user can see, so the newest entry always has an item.
 // releaseNotes.test.ts holds that, the version against VERSION, the length and the HU/EN parity, and
 // scripts/gen-changelog.mjs renders the English file as CHANGELOG.md.