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/PlayerModal.dom.test.tsx

@@ -1,7 +1,7 @@
 // @vitest-environment jsdom
 //
 // The YouTube player modal, rendered for real. Its pure helpers (afterRemoval, the progress cache)
-// had tests; what the modal DOES with them had none — a deep-review of the 2026-09 bug hunt found
+// had tests; what the modal DOES with them had none — a review during the 2026-09 bug hunt found
 // that deleting the lines that apply them left every lane green.
 //
 // `window.YT` is a fake installed before the module's API loader first runs (that loader memoises
@@ -293,9 +293,9 @@ describe("PlayerModal — toasts raised while it is open", () => {
 });
 
 // --- the dialog contract it now shares (ui/dialogFocus) -----------------------------------------
-// Until E11 this was the one `aria-modal` shell with no accessible name, no Tab trap and no focus
+// This was once the one `aria-modal` shell with no accessible name, no Tab trap and no focus
 // restore: Tab walked out of an open player into the page behind the scrim, and closing it with
-// Escape left a keyboard user on <body>, their place in a long feed lost (deep-review round 7).
+// Escape left a keyboard user on <body>, their place in a long feed lost.
 describe("PlayerModal — the dialog contract", () => {
   const open = (onClose = () => {}) => {
     vi.spyOn(api, "videoDetail").mockReturnValue(new Promise(() => {}));
@@ -444,7 +444,7 @@ describe("PlayerModal — the side arrows", () => {
   });
 });
 
-// E31 S1: at 133% zoom (a 685px window) a full-width card ran 20px past the bottom and cut its channel
+// At 133% zoom (a 685px window) a full-width card ran 20px past the bottom and cut its channel
 // row. The card's width is capped from the window height less what sits under the video, measured.
 describe("PlayerModal — fits the window's height", () => {
   it("caps the card's width by the chrome measured under the video", () => {
@@ -469,7 +469,7 @@ describe("PlayerModal — fits the window's height", () => {
   });
 });
 
-// E31 (the owner's pick "A"): on a wide window the video was capped at ~1008 px of a 1920 screen, with
+// The owner's pick: on a wide window the video was capped at ~1008 px of a 1920 screen, with
 // empty space all round. From 1280 px the title, channel, actions, description and queue sit in a side
 // panel beside the video, and the video takes the window's height.
 describe("PlayerModal — the side panel on a wide window", () => {
@@ -542,7 +542,7 @@ describe("PlayerModal — the side panel on a wide window", () => {
     expect(spin(document.querySelector(".player-stage")!, 100)).toBe(true); // over the video
   });
 
-  // E31 S5: a failed load read "No description." in the always-open panel — an error drawn as empty.
+  // A failed load read "No description." in the always-open panel — an error drawn as empty.
   it("says the description failed to load, with a retry, instead of 'No description'", async () => {
     wideWindow(true);
     const detail = vi
@@ -563,7 +563,7 @@ describe("PlayerModal — the side panel on a wide window", () => {
     expect(detail).toHaveBeenCalledTimes(2);
   });
 
-  // E31 review 2: the popover below 1280 px said it the same way only by a copy nobody tested.
+  // The popover below 1280 px said it the same way only by a copy nobody tested.
   it("says it in the description popover below 1280 px too", async () => {
     wideWindow(false);
     vi.spyOn(api, "videoDetail").mockRejectedValue(new Error("boom"));