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/designSystems.ts

@@ -1,5 +1,5 @@
 /**
- * Design systems — the stylesheet held as records (milestone #254).
+ * Design systems — the stylesheet held as records.
  *
  * A design system is a named set of tokens with an optional parent. A system
  * with no parent is a "family"; one with a parent holds ONLY what it changes,
@@ -82,8 +82,8 @@ export interface StarterRoleGroup {
 }
 
 /** The starter token ROLES offered at creation — names and purposes, never
- *  values. A default palette would be one install's taste shipped as product
- *  (rule #115), so the values are always the operator's to fill. */
+ *  values. A default palette would be one install's taste shipped as product,
+ *  so the values are always the operator's to fill. */
 export const listStarterRoleGroups = () =>
   apiGet<{ groups: StarterRoleGroup[]; default_prefix: string }>(
     "/api/design-systems/starter-roles",