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.

frontend/src/design-lab/batchCActions.tsx

@@ -5,9 +5,9 @@ import { LAYER } from "./labTokens";
 import { iconButtonClass } from "../components/ui/buttonStyles";
 import { SURFACE } from "../components/ui/surfaces";
 
-// E28 S2 · Batch C, part 1 — action placement: the classification table (object × action → where it
-// lives), DECIDED (owner, 2026-09-24: accepted as proposed). It is the source S3 builds each object's
-// ONE action list from. It applies
+// Batch C, part 1 — action placement: the classification table (object × action → where it
+// lives), DECIDED (owner, 2026-09-24: accepted as proposed). It is the source each object's
+// ONE action list is built from. It applies
 // the decided guard rails (DESIGN.md "Action placement"): ONE action list per object feeds every
 // trigger; the primary action and visible state stay on the object; rare, secondary and destructive
 // actions go to the menu; nothing is gesture-only, because the "…" button opens the same menu.
@@ -19,7 +19,7 @@ type Row = {
   mouse: Where;
   /** touch card / row: visible, or reached through "…" */
   touch: "visible" | "…";
-  /** what changes against today (the S2 inventory), empty when nothing does */
+  /** what changes against today's actions, empty when nothing does */
   change?: string;
   danger?: boolean;
 };