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/query.py

@@ -31,9 +31,9 @@ PLEX_SORT_KEYS: tuple[str, ...] = (
     "title",
 )
 
-# --- Language-aware column pickers (E5 S6) ----------------------------------
+# --- Language-aware column pickers ----------------------------------
 #
-# The HU-overlay twin (E5 S5) stores Hungarian metadata in `*_hu` columns on the SAME EN row. When
+# The HU-overlay twin stores Hungarian metadata in `*_hu` columns on the SAME EN row. When
 # the app language is `hu` we serve those, falling back to the EN column where a row has no HU twin.
 # Two flavours of picker, on purpose:
 #   * DISPLAY / FILTER (`title_col`/`genres_col`): `coalesce(*_hu, *)` — an EN fallback so a row with
@@ -41,8 +41,8 @@ PLEX_SORT_KEYS: tuple[str, ...] = (
 #     HU summary directly off the loaded row, so no `summary_col` SQL helper is needed.)
 #   * SEARCH (`vector_col` + `field_recheck`): the raw `*_hu` column coalesced to '' — MIRRORING the
 #     generated `search_vector_hu` definition (which uses `coalesce(title_hu, '')`, NOT an EN
-#     fallback), so the field recheck stays a strict subset of the GIN vector prefilter (the S2
-#     invariant). `people_text` is language-neutral and shared by both vectors.
+#     fallback), so the field recheck stays a strict subset of the GIN vector prefilter (the
+#     field-search invariant). `people_text` is language-neutral and shared by both vectors.
 
 
 def title_col(model, lang: str):
@@ -216,7 +216,7 @@ def meta_filter_conds(model, p: dict, lang: str = "en") -> list:
     stds = split_csv(p.get("studios"))
     if stds:  # OR
         conds.append(model.studio.in_(stds))
-    for kw in split_csv(p.get("keywords")):  # AND — TMDB keyword chips from the detail page (E5 S5)
+    for kw in split_csv(p.get("keywords")):  # AND — TMDB keyword chips from the detail page
         conds.append(model.keywords.contains([kw]))
     csel = split_csv(p.get("collections"))
     if (
@@ -232,7 +232,7 @@ def apply_meta_filters(q, model, p: dict, lang: str = "en"):
     return q.where(*conds) if conds else q
 
 
-# --- Playback-class filter (E7) — MOVIE-ONLY (a show is an aggregate with no single class) ---------
+# --- Playback-class filter — MOVIE-ONLY (a show is an aggregate with no single class) ---------
 # The 4 classes the feed filter + facet expose, derived from the stored `playable` + `transcode_hw`.
 # ONE definition (this SQL CASE) so the filter WHERE and the facet counts can't drift: `playable_conds`
 # filters on it, `facets` groups by it. transcode_hw IS NOT True groups NULL (unprobed) with software.
@@ -278,7 +278,7 @@ class LibraryFilters:
     actors: str | None = None
     actor_mode: str = "any"  # how multiple actors combine: any (OR, default) | all (AND)
     studios: str | None = None
-    keywords: str | None = None  # TMDB keyword chips (E5 S5), CSV; language-neutral
+    keywords: str | None = None  # TMDB keyword chips, CSV; language-neutral
     collections: str | None = None  # CSV of collection rating_keys
     collection_mode: str = "any"  # how multiple collections combine: any (OR, default) | all (AND)
     playable: str | None = None  # CSV of playback classes: direct|remux|transcode_hw|transcode_sw
@@ -311,7 +311,7 @@ class LibraryFilters:
 # watch state. The SAME predicate has to be applied in two places — `unified_library` (the grid) and
 # `facets.wsq` (so the facet counts reflect exactly the visible set) — and they MUST stay identical:
 # a hidden movie kept out of the grid must not inflate the facets either. These helpers are the one
-# home for that predicate so the two call sites can't drift (E3 S1; pinned by test_plex_facets_grid_
+# home for that predicate so the two call sites can't drift (pinned by test_plex_facets_grid_
 # parity). Callers pass the already-joined state expressions, so this module stays model-agnostic:
 #   * movies — `st` is an aliased PlexState outer-joined on (item_id, user_id).
 #   * shows  — `tot`/`wat`/`inp` are the coalesced totals from `rollup.agg_subquery`.
@@ -367,9 +367,9 @@ def apply_show_state_filter(query, tot, wat, inp, show: str):
 def content_libs(db: Session) -> tuple[list[int], list[int]]:
     """The BROWSABLE content libraries, partitioned into (movie_lib_ids, show_lib_ids) — the single
     source of the browse scope. Excludes HU overlay libraries (`overlay_of` set): those are never
-    browsed on their own, they only lend their Hungarian metadata to the EN twin's rows (E5 S5).
+    browsed on their own, they only lend their Hungarian metadata to the EN twin's rows.
 
-    Lives here, in the query layer, rather than in `routes/plex/_shared.py` where it started: E24's
+    Lives here, in the query layer, rather than in `routes/plex/_shared.py` where it started: the
     Home surface needs the same scope, and a domain package importing from `routes/` would invert the
     one-way dependency CLAUDE.md draws. It never touched request state, so nothing was lost by the
     move."""