docs(6208): the remaining frontend comments drop milestone, step and rule citations

Components, stores, api clients, router, types and shared CSS now state what
each piece is and why, without the milestone that introduced it. diff.ts
names its consumers instead of the copy history; stores/notes and tasks state
their current scope instead of the cleanup that set it; theme.css states the
token practice instead of the sweep that established it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/api/client.ts

@@ -55,7 +55,7 @@ export function apiErrorMessage(e: unknown, fallback: string): string {
 /**
  * How long an ordinary JSON call may wait before it is declared failed.
  *
- * Rule 156: a wait with no deadline is a bug. `fetch`'s own default is to wait
+ * A wait with no deadline is a bug. `fetch`'s own default is to wait
  * as long as the browser will, which is not a deadline — it is the absence of
  * one, and it renders as a spinner that never resolves. There is no state a
  * surface can show for "pending forever" that is not a lie.
@@ -118,7 +118,7 @@ export interface RequestOpts {
  * The one place a request is actually made — every verb below goes through
  * here, so the deadline cannot be forgotten by adding a sixth.
  *
- * EXPIRY SURFACES AS AN `ApiError`, which is rule 156's second half: the
+ * EXPIRY SURFACES AS AN `ApiError`, the deadline's second half: the
  * failure has to arrive in the shape the caller already handles. A bare
  * `DOMException: TimeoutError` would reach `apiErrorMessage(e, fallback)` as
  * an object with no `body`, so every catch site in the app would report its