feat(ui): show a user icon in the profile menu trigger

[a-effort]

What

Add icon to user settings dropdown:

before	after
empty size-6 box + chevron	user icon in the same box + chevron

Theming

Colors come from the muted / muted-foreground tokens, which index.css redefines under .dark. Lucide icons stroke with currentColor, so light and dark need no conditional logic and no dark: variants. They use the same pairing the neighboring GitHub and docs icons in the header already use.

A test asserts the fallback className contains no dark: prefix, so a future hardcoded override trips a test instead of shipping.

Structuring for profile pictures later

UserAvatar owns the fallback ladder rather than HeaderProfileMenu inlining an icon, and takes an optional src.

Worth knowing: there is no avatar/picture field anywhere in the API... checked openapi.json, src/generated/types/contextForge.ts and src/types/user.ts. So, profile pictures need a backend field first; this isn't a frontend-only follow-up. The seam is here because Radix Avatar is what handles the image load/error swap, which is the awkward part to retrofit later. An initials leg (from full_name) is the middle step that needs no backend at all.

The primitive comes from the radix-ui umbrella package, already a dependency (no new dependencies added). Sizing stays size-6 rounded-md with overflow-hidden, so an image later fills the same box and the header geometry doesn't move.

Accessibility / i18n

The trigger button already carries aria-label={displayName}, so the icon is decorative: aria-hidden, no second accessible name, and no new i18n strings.

Tests

• avatar.test.tsx, user-avatar.test.tsx
• HeaderProfileMenu.test.tsx

Note UserAvatar's src path can't be exercised in jsdom: Radix builds an off-DOM Image and waits for load, which jsdom never fires, so the <img> never mounts. The test asserts what is meaningful there: passing a src neither crashes nor blanks the frame and says why inline. Image rendering needs an e2e check once the backend field exists.

tsc -b / eslint / prettier   clean
vitest                       167 files, 2908 passed, 1 skipped

⚠️ Merge order

Based on fix/vendor-chunk-cycle (#45)... do not merge this first.

This change shifts chunk composition enough to trip a latent rollup chunk cycle that #45 fixes. Without #45 the app serves a blank page (Cannot set properties of undefined (setting 'Activity')). I verified both directions: this commit without #45 fails a module-eval smoke test, with #45 it passes.

No CI job runs npm run build, and E2E drives the Vite dev server where manualChunks doesn't apply, so this PR goes green either way. The ordering has to be enforced by hand. Retarget to main once #45 merges; no rebase needed.