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/ruff.toml

@@ -1,7 +1,7 @@
 # Ruff config for the Siftlode backend. Keeps ruff's default rule set (E4/E7/E9 + F = the
 # high-signal pyflakes/pycodestyle checks that catch real dead code + bugs), all of it on. E402 was
-# ignored for main.py's logging setup; the ignore had let 11 incidental late imports in elsewhere
-# (E32 review), so it is on now and main.py marks each deliberate one (`# noqa: E402 — <why>`).
+# ignored for main.py's logging setup; the ignore had let 11 incidental late imports in elsewhere,
+# so it is on now and main.py marks each deliberate one (`# noqa: E402 — <why>`).
 # `scripts/e2e_seed.py` edits `sys.path` before its imports, which E402 itself allows.
 #
 # line-length 100 (ruff's default is 88): matches the frontend prettier printWidth so both halves of
@@ -14,7 +14,7 @@ line-length = 100
 target-version = "py312"
 
 [lint]
-# Beyond the default set, the rules that hold a LOG LINE to what E22.5 makes of it:
+# Beyond the default set, the rules that hold a LOG LINE to what the log pipeline makes of it:
 #   LOG     — stdlib logging misuse (`.warn()`, a logger built by hand, `exc_info` on `.exception`)
 #   G       — the call's shape: %-style args, never an f-string the level filter cannot skip, and
 #             never `str(exc)` where `exc_info` would carry the traceback
@@ -32,11 +32,11 @@ target-version = "py312"
 # The wider rule these two enforce lives in tests/test_swallowed_exceptions.py: a handler that
 # neither logs nor re-raises says `# silent-ok: <why>`. Ruff sees only the two narrow shapes.
 #
-# E32 (gate integrity) added three more, each measured before it went on and with every hit fixed:
+# Gate integrity added three more, each measured before it went on and with every hit fixed:
 #   RUF100  — a `# noqa` that suppresses nothing. A stale one is a claim with no rule behind it, and
 #             it stays armed for the day the line changes (24 were removed). A comment that merely
 #             explains a noqa below it names the rule as `# TRY400: …`, never `# noqa TRY400`.
-#   PLW1510 — `subprocess.run` without an explicit `check=`. Found the real E32 bug: three ffprobe
+#   PLW1510 — `subprocess.run` without an explicit `check=`. Found a real bug: three ffprobe
 #             probes read the output of a probe that had FAILED and took it for the file's truth.
 #   B       — flake8-bugbear: loop-variable capture, `raise` without `from` inside `except`, a
 #             `zip` that silently truncates (each one is `strict=True` now — the lengths are an