Ship Hesychia meander logo for rebrand (#30) (#46)

## Summary
Closes #30.

- Replace old infinity brand mark with the cyan Greek-key (meander) Hesychia emblem
- Update web favicons / PWA icons (`public/`), Capacitor source art (`assets/`), and regenerate Android launcher + splash densities
- Wire mark into Header / Header2, Sign In / Sign Up, and Sidenav branding

## Test plan
- [ ] Favicon + apple-touch icon show new mark in browser tab / home screen
- [ ] Header and auth screens show mark + Hesychia wordmark
- [ ] `npm run assets:generate` already run; Android launcher / splash use new art
- [ ] Old infinity artwork no longer present in `assets/` / `public/` brand slotsReviewed-on: #46

llm-fe/ANDROID.md

@@ -50,7 +50,14 @@ Bump both before each store release.
 
 ## Icons / splash
 
-Source art lives in `llm-fe/assets/` (`icon.png`, `splash.png`, `splash-dark.png`). Regenerate Android densities:
+Source art lives in `llm-fe/assets/`:
+- `icon.png` / `splash.png` / `splash-dark.png` — Capacitor inputs (Hesychia meander mark)
+- `logo-source.png` — cropped square master
+- `logo-mark-transparent.png` — circular mark with transparent corners (web / in-app)
+
+In-app UI also imports `src/llm-fe/assets/brand/hesychia-mark.png`.
+
+Regenerate Android densities after changing source art:
 
 ```bash
 npm run assets:generate