feat: add Headquarter favicon

- Add a geometric evergreen Headquarter mark for browser tabs\n- Register the SVG favicon and matching browser theme color\n\nOpenSpec: add-project-favicon\nQuality gates: npm run build

openspec/changes/add-project-favicon/change.md

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+# Add a Headquarter Favicon
+
+## Summary
+
+Add a compact, recognizable favicon for Headquarter and register it in the web document head.
+
+## Design
+
+Use a geometric cream `H` on the product's evergreen brand field. The mark remains identifiable at small browser-tab sizes, avoids font rendering dependencies, and matches both light and dark application themes.
+
+## Scope
+
+- `apps/web/public/favicon.svg`
+- `apps/web/index.html`
+
+## Acceptance Criteria
+
+- [ ] The browser uses a dedicated Headquarter favicon.
+- [ ] The mark remains legible at small sizes and on light or dark browser chrome.
+- [ ] The HTML declares the icon type and a matching browser theme color.
+- [ ] Frontend production build passes.

openspec/changes/add-project-favicon/tasks.md

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+# Add a Headquarter Favicon — Tasks
+
+- [x] Create the favicon asset.
+- [x] Register the favicon and browser theme color in the web entry document.
+- [x] Run the frontend production build.
+- [x] Update project maps for changed source files.