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.

backend/app/plex/overlay.py

@@ -1,5 +1,5 @@
-"""The HU overlay: a Hungarian Plex section written onto its English twin's rows (E30), split out of
-`plex/sync.py` (E32 S2), which runs it once per paired section during the full sync.
+"""The HU overlay: a Hungarian Plex section written onto its English twin's rows, split out of
+`plex/sync.py`, which runs it once per paired section during the full sync.
 
 The pairing is admin-configured (`plex_overlay_map`, ``huKey:enKey,...``). An overlay section creates
 no browsable rows of its own; it only fills the `*_hu` columns of the EN rows it matches by guid.
@@ -41,7 +41,7 @@ def sync_overlay(
     """Write an overlay section's Hungarian metadata onto its EN twin's rows, matched by guid. Creates
     NO browsable rows — an overlay library is never listed on its own. Only title/summary/tagline/genres
     differ by language; the language-neutral people_text feeds both search vectors. A show section's
-    episodes are overlaid too (E30): the HU section lists every episode with its Hungarian title and
+    episodes are overlaid too: the HU section lists every episode with its Hungarian title and
     summary, and the episode rows live in the EN show library.
 
     This is a full RECONCILE: after a COMPLETE HU listing every guid-bearing EN row's HU fields are
@@ -141,7 +141,7 @@ def _clear_hu(by_guid: dict, episodes: bool) -> None:
     cheap. The genres are the exception: every row gets Hungarian ones, from its HU twin or, lacking
     one, from its own English list — otherwise the HU genre list mixed "Drama" (no twin) with "Dráma".
     Only after a COMPLETE listing: one a Plex hiccup cut short would clear the HU text of every title
-    it failed to reach, until the next full sync (E32 S2, the watch reconcile's twin)."""
+    it failed to reach, until the next full sync (the watch reconcile's twin)."""
     for group in by_guid.values():
         for row in group:
             row.title_hu = row.summary_hu = None