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/App.vue

@@ -13,11 +13,10 @@ import { fetchVersion } from "@/api/version";
 useTheme();
 
 const router = useRouter();
-// THREE states, not two (#3127 checklist 12). `null` is "not answered yet" and
-// renders nothing; a string renders; `appVersionFailed` renders its own thing.
-// This used to default to the literal "dev" and swallow the error, which meant
-// an instance that could not answer was indistinguishable from a local build
-// that genuinely reports "dev" — a blank standing in for `unknown`, in the one
+// THREE states, not two. `null` is "not answered yet" and renders nothing; a
+// string renders; `appVersionFailed` renders its own thing. Defaulting to the
+// literal "dev" and swallowing the error would make an instance that cannot
+// answer indistinguishable from a local build that genuinely reports "dev" — a blank standing in for `unknown`, in the one
 // readout whose whole job is to say what is running.
 const appVersion = ref<string | null>(null);
 const appVersionFailed = ref(false);