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/adminInvites.dom.test.tsx

@@ -72,7 +72,7 @@ vi.mock("../lib/api", async (importOriginal) => {
       adminInvites: () => listMock(),
       deleteInvite: (id: number) => deleteMock(id),
       sendInvitation: (id: number, lang: string) => inviteMock(id, lang),
-      // The access tab also renders the stuck-sign-ups section (E9.5 S5); nothing stuck here, so it
+      // The access tab also renders the stuck-sign-ups section; nothing stuck here, so it
       // renders nothing and this file stays about the delete affordance.
       adminPendingAccess: () => Promise.resolve([]),
     },
@@ -164,7 +164,7 @@ describe("Access requests — the delete affordance", () => {
     await openAccessTab();
 
     fireEvent.click(await screen.findByText(/settings\.invites\.decided/));
-    // E30: the decision is named, not the raw status word ("denied").
+    // The decision is named, not the raw status word ("denied").
     expect(screen.getByText("settings.invites.status.denied")).toBeTruthy();
     expect(screen.queryByText("denied")).toBeNull();
     fireEvent.click(await screen.findByLabelText("settings.invites.deleteLabel:asker@example.com"));
@@ -243,7 +243,7 @@ describe("Access requests — the delete affordance", () => {
 
 // Whitelisting an address is opening a door as a possibility, not knocking on one — the operator has
 // usually already agreed it with the person, and a row can sit approved for weeks. So adding stays
-// silent and telling them is its own act, on its own button (E9.5 S6).
+// silent and telling them is its own act, on its own button.
 describe("inviting someone the admin whitelisted", () => {
   // The decided rows live behind a <details>; await the summary rather than the section title, or
   // the click races the invite query that populates it.
@@ -317,7 +317,7 @@ describe("inviting someone the admin whitelisted", () => {
     expect(dialog.container.textContent).toContain("settings.invites.inviteConfirmAgain");
   });
 
-  it("dates the earlier invite in the admin's language, not the invitee's (E30 review)", async () => {
+  it("dates the earlier invite in the admin's language, not the invitee's", async () => {
     listMock.mockResolvedValue([
       invite({ status: "approved", invited_at: "2026-09-05T09:00:00Z", lang: "hu" }),
     ]);