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/scheduler.py

@@ -154,7 +154,7 @@ def _audit_run(db, actor_id, job_id, status, summary, result) -> None:
     they changed something, so routine no-op polls don't spam the trail. Best-effort."""
     if actor_id is None and status == "ok" and not _run_changed(result):
         return
-    # The result as data too (E30): the audit log names it in the reader's language, as the inbox
+    # The result as data too: the audit log names it in the reader's language, as the inbox
     # does; `summary` stays the English line of the row's own summary column.
     data = _result_data(result)
     try:
@@ -252,7 +252,7 @@ _PAUSED = {"skipped": "sync paused"}
 
 
 def _result_data(result) -> dict | None:
-    """A job's result as the client names it in the reader's language (E30): the dict itself (counts,
+    """A job's result as the client names it in the reader's language: the dict itself (counts,
     a `skipped` / `reason` word, a nested dict per phase), `enrich`'s bare count as one. The one-line
     `_summarize` is the English fallback."""
     if isinstance(result, dict):
@@ -401,7 +401,7 @@ def _tmdb_enrich_job() -> None:
 
 
 def _people_enrich_job() -> None:
-    # Make the people local (E30 S6): a batch of person bios from TMDB and a batch of portraits resized
+    # Make the people local: a batch of person bios from TMDB and a batch of portraits resized
     # through Plex, so a person page and a cast strip never wait on an outside service.
     _job("people_enrich", run_people_enrich)
 
@@ -428,7 +428,7 @@ def _log_gc_job() -> None:
 
         days = sysconfig.get_int(db, "log_retention_days")
         reaped = logsink.gc(db, days)
-        # Debug sessions (E16) go with the rows they bundle; an open one past its cap is closed.
+        # Debug sessions go with the rows they bundle; an open one past its cap is closed.
         closed = debugsession.sweep(db)
         sessions = debugsession.gc(db, days)
         db.commit()