feat: adopt brand lockup + canonical icons (ui#29 wave 2)

[rep0x]

Summary

Wave 2 brand-refresh fan-out (MIND-Studio/ui#29) for the chat repo. Pattern from the approved drive pilot (drive#17). Based on the open @mind-studio/ui 0.7.0 bump branch (chore/ui-0.7.0-brand-refresh) so the new <Logo label="..."> prop and the React-free ./brand subpath (MIND_MARK_SVG, MIND_GREEN, monoMarkSvg, …) are available. Base = the bump branch, so this diff is just the Wave 2 work.

What changed

Tier 3 — in-app logo lockup (src/app/page.tsx)

• The home page header's bare mind/chat text wordmark (<h1>) is replaced with <Logo label="Chat" /> — the shared weave mark + Chat set in the brand serif (Fraunces). Chat has no persistent masthead/footer (its layout delegates to <ThemeShell>), so the home page header is the most prominent visible brand surface.
• Logo added to the @mind-studio/ui import.

Tier 4 — canonical static brand assets (mark-only, generated from @mind-studio/ui/brand)

• scripts/gen-icons.mjs — generates the favicon + PWA/apple-touch icons from the canonical mark (MIND_MARK_SVG / monoMarkSvg / MIND_GREEN), so they can never drift from the published logo. Adapted from drive; same four outputs, Chat header comment.
• src/app/icon.svg — replaces the hand-rolled cyan/magenta speech-bubble placeholder with the canonical gradient weave mark.
• src/app/apple-icon.png (180), public/icon-192.png, public/icon-512.png — generated maskable/apple-touch binaries, committed.
• src/app/manifest.ts — name: "Mind Chat", short_name: "Chat", Chat description, theme_color: "#16B88A", background_color: "#07080b".
• src/app/opengraph-image.tsx — dark green-glow share card with the MIND_MARK_SVG mark + Chat wordmark and Chat-appropriate copy. Deterministic (default font, no remote fetch).
• package.json — + "gen:icons" script, + sharp ^0.34.5 devDependency (npm / package-lock.json).

Next 16 auto-detects all four assets by file convention (/icon.svg, /apple-icon.png, /manifest.webmanifest, /opengraph-image all appear in the build route table) — no manual metadata wiring needed, and layout.tsx had no conflicting hard-coded icons.

Test plan

All run from the worktree with NODE_AUTH_TOKEN=$(gh auth token):

Command	Result
npm run gen:icons (×2)	✅ reproducible — PNGs byte-identical on re-run
npm run typecheck	✅ pass
npm run lint	✅ exit 0 (only pre-existing warnings/infos; none in the new files)
npm run test	✅ pass (no test files; --passWithNoTests)
npm run build	✅ pass — /icon.svg, /apple-icon.png, /manifest.webmanifest, /opengraph-image all in route table

Pre-existing note (not introduced here): build warns metadataBase is unset for resolving social OG/Twitter image URLs — same as the drive pilot; OG image still generates.

Note

Wave 2 fan-out, pattern from drive#17. Repo-specific wrinkles vs drive:

• chat has NO *.png ignore rule, so the generated icon binaries commit normally — no .gitignore negations needed (unlike drive).
• chat had no public/ directory — created it so the maskable PNGs land at the served root (the manifest references /icon-192.png and /icon-512.png).
• Tier 3 surface is the home page header, not a masthead/footer (chat has neither).

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