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/components/ui/anchoredPopoverHooks.ts

@@ -23,7 +23,7 @@ import {
 import { useLayer } from "../../lib/layerStack";
 import { pageStep, pageTarget, scrollParent } from "../../lib/listPaging";
 
-// The non-component half of the R8 popover platform: the `useAnchoredPopover` engine hook and the
+// The non-component half of the popover platform: the `useAnchoredPopover` engine hook and the
 // `closeThenAct` row helper. The surfaces it drives (PopoverSurface / PopoverItem) and the platform's
 // design notes live in AnchoredPopover.tsx; the split keeps that file components-only (Fast Refresh).
 
@@ -69,13 +69,13 @@ export interface AnchoredPopoverOptions {
   /** Close when a scroll container under the panel scrolls. Off by default, because a panel anchored
    *  to a real trigger element simply MOVES with it. Turn it on when the anchor is a fixed point
    *  rather than an element — a right-click menu, which otherwise stays parked over whatever row
-   *  scrolls under it while its actions still target the row you opened it on (E10 review round 1).
+   *  scrolls under it while its actions still target the row you opened it on.
    *  This is also what a native context menu does. */
   dismissOnScroll?: boolean;
   /** Menu/listbox only: ↑/↓ on the CLOSED trigger open the panel (the APG menu-button default, on).
    *  Turn it off where those keys already mean something on that trigger — a media player's row,
-   *  where ↑/↓ are the volume from anywhere, and a trigger that swallowed them killed it (E28 review
-   *  round 2, P2). Enter/Space/click still open it, and the arrows still rove once it is open. */
+   *  where ↑/↓ are the volume from anywhere, and a trigger that swallowed them killed it.
+   *  Enter/Space/click still open it, and the arrows still rove once it is open. */
   openOnArrowKey?: boolean;
 }
 
@@ -308,7 +308,7 @@ export function useAnchoredPopover(opts: AnchoredPopoverOptions) {
 /** A menu row whose action opens a dialog or moves the focus: close the menu FIRST and act once it
  *  has handed the focus back. floating-ui returns the focus to the trigger from a microtask queued as
  *  the menu unmounts, so an action run in the same batch had its focus taken back by it: measured in
- *  Chrome (E11 S2), a confirm dialog opened from the rail's menu landed its focus on Cancel and lost it
+ *  Chrome, a confirm dialog opened from the rail's menu landed its focus on Cancel and lost it
  *  7 ms later to the row BEHIND its scrim, where Enter activated the row. A fresh task runs after that
  *  microtask — and a dialog opened there captures the trigger, not a dying menu item, as the element
  *  to restore the focus to. Every such row goes through here (`ActionMenu`, "Manage views…"). */