Add TypeScript migration, image resizing, media upload UX, and multimedia support

- Migrate static JS to TypeScript (static-ts/ → compiled to internal/api/static/)
- Add image resizing on upload: JPEG/PNG/WebP scaled to max 1920px at quality 80
- Extract shared upload logic into upload.go (saveUpload, saveResizedImage, saveResizedWebP)
- Add POST /media endpoint for drag-drop/paste media uploads with markdown ref return
- Add background music player with video/audio coordination (autoplay.ts)
- Add global nav, public feed, hashtags, visibility, Markdown rendering for entries
- Add Dockerfile stage for TypeScript compilation (static-ts-builder)
- Add goldmark, disintegration/imaging, golang.org/x/image dependencies

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -62,8 +62,23 @@ internal/
     ingest.go     POST /v1/trackpoints, POST /v1/trackpoints:batch
     query.go      GET /v1/days, /v1/trackpoints, /v1/stops, /v1/suggestions
     webui.go      server-side rendered web UI (login, /days, /days/{date})
-    journal.go    journal entry endpoints
+    journal.go    POST /entries, GET/POST /entries/{id}, GET /entries/{id}/edit
+    media.go      POST /media — single-file upload, returns markdown reference
     response.go   shared response helpers
+  api/static/
+    style.css     global styles (Pico CSS overrides)
+    day.js        GPS button, time auto-fill
+    editor.js     textarea drag-drop/paste upload → markdown ref insert
+    autoplay.js   IntersectionObserver: videos autoplay when visible
+  api/templates/
+    base.html     layout + global nav (LoggedIn, IsAdmin injected by render())
+    days.html     day list + date picker
+    day.html      day detail: new entry form, entries, stops, trackpoints
+    edit_entry.html  edit existing entry
+    public.html   public feed (infinite scroll)
+    login.html    login form
+    register.html self-registration
+    admin/        admin layout + entries/users pages
 ```
 
 Key invariants: