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/feedquery.py

@@ -109,7 +109,7 @@ def _tag_visible(user: User):
 # The pseudo-category of a selected tag id no Tag row answers (a saved view or the feed state outlives
 # a deleted tag). It filters like a category whose tags no channel carries — to nothing, in the SQL and
 # in feed_summary's mirror alike — instead of the id being dropped, which showed the WHOLE feed under
-# the view's old name (E32 S2). No real category is called this (language/topic/other).
+# the view's old name. No real category is called this (language/topic/other).
 MISSING_TAG_CATEGORY = "missing"
 
 
@@ -118,7 +118,7 @@ def tags_by_category(db: Session, user: User, tag_ids: list[int]) -> dict[str, l
     shared by the feed's tag WHERE (filtered_query) and the facet/count summary (feed_summary), so the
     two can't disagree on which selected tag belongs to which category. An unknown id lands in
     MISSING_TAG_CATEGORY — and so does another user's private tag: resolving it to its real category
-    told the caller which foreign ids exist (E32 review)."""
+    told the caller which foreign ids exist."""
     if not tag_ids:
         return {}  # skip the pointless `WHERE id IN ()` round-trip on the no-tag-filter hot path
     out: dict[str, list[int]] = {}
@@ -463,7 +463,7 @@ def feed_summary(db: Session, user: User, **params) -> dict:
 
 
 def feed_years(db: Session, user: User, **params) -> list[dict]:
-    """Per-year video counts for the current filter context (item 8 / E8·S2): powers the year control's
+    """Per-year video counts for the current filter context: powers the year control's
     quick chips + the "more…" per-year-counts dialog. Every OTHER filter (tags, channels, content type,
     search, watch state, scope) still applies, but the publish-date narrowing itself is DROPPED —
     published_after/before and max_age_days — so the year list is the full set of years available and
@@ -559,7 +559,7 @@ def sort_keys(sort: str, seed: int, rank_expr=None, lang: str | None = None) ->
     return table.get(sort) or table["newest"]
 
 
-# Relevance ranks only the newest RANK_WINDOW matches (E31): ts_rank reads every match's tsvector, and
+# Relevance ranks only the newest RANK_WINDOW matches: ts_rank reads every match's tsvector, and
 # a broad word matches most of the library ("a" ranked 193k rows in 6.8 s on prod, against 1.1 s to just
 # find them). The rows past the window keep rank 0, so they follow the ranked ones newest first; a word
 # that broad has no meaningful relevance order anyway, and a specific one fits the window whole.
@@ -671,7 +671,7 @@ def encode_cursor(keys: list[dict], row, window: datetime | None = None) -> str:
 def _cursor_dt(v):
     """A cursor's timestamp: aware or refused. The server writes only aware ones (timestamptz), and
     windowed_relevance_rows compares them in Python, where a naive one beside an aware one raises — a
-    500 for a hand-made cursor instead of the 400 (E31 review 2)."""
+    500 for a hand-made cursor instead of the 400."""
     if v is None:
         return None
     dt = datetime.fromisoformat(v)