docs(6210): acceptance sweep — src, scripts and frontend leftovers described in the present tense

The acceptance greps found what the per-area passes missed:

- src/scribe: "Phase 7/8" removal notes in projects, settings and
  user_profile; a paragraph promising an auto-summary side effect that no
  longer exists; user_profile's claim that "upcoming MCP profile tools" read
  the profile, which nothing does; an instance count and instance rule
  titles in plugin_context; "MILESTONE 323 DECIDED" in rulebooks.
- scripts/: check_plugin's header and inline comments were a history of
  the incidents behind each guard, with issue numbers in two failure
  messages; check_dangling_styles named this app's classes as its examples;
  check_design_tokens, measure_duplication and mint_plugin_version cited
  issues and checklists.
- frontend/src: forty-odd comments with four-digit issue numbers that the
  earlier frontend scan filtered out as hex colours, plus "used to" and
  "Phase N" notes.

Kept: illustrative ids (`#4181` as a bare-id example, `PR #198`), migration
Create Date headers and one migration's dated data floor, and the plugin
skills' worked examples of how to cite a record.

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

frontend/src/api/client.ts

@@ -41,8 +41,8 @@ async function handleResponse<T>(res: Response, path: string): Promise<T> {
 /**
  * The server's `{"error": "..."}` message from a failed call, or `fallback`
  * when the failure carried none (network error, non-JSON body). The one place
- * the error envelope is unpacked on the client — views used to restate this
- * as a six-line `"body" in e` branch at every catch site.
+ * the error envelope is unpacked on the client, so no view restates it as a
+ * `"body" in e` branch at its catch site.
  */
 export function apiErrorMessage(e: unknown, fallback: string): string {
   if (e && typeof e === "object" && "body" in e) {
@@ -61,8 +61,7 @@ export function apiErrorMessage(e: unknown, fallback: string): string {
  * surface can show for "pending forever" that is not a lie.
  *
  * 30s is chosen to be longer than anything healthy: it has to clear a cold
- * embedding call and a list view under connection-pool contention (#2384 had
- * /api/projects fanning 25 concurrent sessions at a 15-connection pool), so
+ * embedding call and a list view under connection-pool contention, so
  * tripping it means something is genuinely wrong rather than merely busy. Slow
  * BY DESIGN is a different case and passes its own value — see the callers in
  * SettingsView that do.