chore: voice + filename hygiene + wave-4 state wrap

Maintainer-voice sweep across `src/`. ~190 references to the
maintainer by first name in code comments and JSDoc neutralised to
"the maintainer", "the live tenant", "users", or "the user" depending
on context. Three sed passes covering ~50 distinct patterns
(`Marc reported`, `Marc wants`, `Marc kept`, `Marc rolled back`, etc.).
Test fixtures (`displayName: "Marc B."`, `username: "marc"`,
`<HeroStrip userName="Marc">`) kept as opaque test data per the brief.

CHANGELOG normalisation. The v1.4.14 + v1.4.15 entries paired a
German bullet with its English translation by historical design — the
in-app copy is English-default and the user docs are English, so the
mixed-language style was a holdover from the early-marathon notes.
A one-off node script extracted the `_..._` English paragraph from
each bilingual bullet and rewrote the entry as that text. ~44 bullets
reduced; one Docs bullet that lost a leading word in the regex
fixed by hand.

CLAUDE.md → CONTRIBUTING-AI.md rename so the filename is no longer
AI-vendor-specific. `CONTRIBUTING.md` reference updated. `AGENTS.md`
stays in place for multi-agent compatibility (the conventions doc is
shared with Codex / Cursor / etc.).

Wave-4 state wrap. STATE.md now records C1–C5 + D + D2 as complete;
v1421-backlog.md grew a "Closed in v1.4.22" header listing the 20
items the marathon landed; `.planning/phase-W4-report.md` documents
the per-commit decisions, test deltas, and the 23 items deferred to
v1.4.23 with reasoning.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/admin/admin-shell.tsx

@@ -153,7 +153,7 @@ export function AdminShell({ active, children }: AdminShellProps) {
           painted scrollbar at the top of every admin page; the
           horizontal swipe + keyboard arrow scrolling still work, the
           bar just doesn't draw. Without this the 13-section strip
-          would render an always-on scrollbar that Marc kept
+          would render an always-on scrollbar that the maintainer kept
           mis-attributing to the api-tokens table below it. */}
       <nav
         aria-label={t("admin.shell.sectionsNav")}