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>

backend/internal/api/templates/edit_entry.html

@@ -14,7 +14,14 @@
       </select>
     </div>
     <input type="text" name="title" placeholder="Überschrift" value="{{.Entry.Title}}">
-    <textarea name="description" rows="4" placeholder="Beschreibung">{{.Entry.Description}}</textarea>
+    <div class="editor-wrap">
+      <textarea name="description" rows="6" placeholder="Beschreibung — Markdown unterstützt&#10;Medien: per Drag & Drop oder Einfügen (Strg+V)">{{.Entry.Description}}</textarea>
+      <div class="editor-bar">
+        <button type="button" class="media-picker">&#128206; Datei anhängen</button>
+        <span class="upload-status"></span>
+        <input type="file" class="media-file-input" multiple accept="image/*,video/*,audio/*" style="display:none">
+      </div>
+    </div>
     <div class="gps-row">
       <input type="number" name="lat" id="entry-lat" step="any" placeholder="Breite"{{if .Entry.Lat}} value="{{printf "%.6f" (deref .Entry.Lat)}}"{{end}}>
       <input type="number" name="lon" id="entry-lon" step="any" placeholder="Länge"{{if .Entry.Lon}} value="{{printf "%.6f" (deref .Entry.Lon)}}"{{end}}>
@@ -23,16 +30,22 @@
     <small id="gps-status"></small>
     <input type="text" name="hashtags" placeholder="Hashtags (kommagetrennt)" value="{{join .Entry.Hashtags ", "}}">
     {{if .Entry.Images}}
-    <div class="entry-images" style="margin-bottom:.5rem">
+    <div class="media-refs">
       {{range .Entry.Images}}
-      <a href="/uploads/{{.Filename}}" target="_blank">
+      <div class="media-ref-row">
+        {{if isVideo .MimeType}}
+        <code class="media-ref-code">![{{.OriginalName}}](/uploads/{{.Filename}})</code>
+        {{else if isAudio .MimeType}}
+        <code class="media-ref-code">[{{.OriginalName}}](/uploads/{{.Filename}})</code>
+        {{else}}
         <img src="/uploads/{{.Filename}}" alt="{{.OriginalName}}" class="thumb">
-      </a>
+        <code class="media-ref-code">![{{.OriginalName}}](/uploads/{{.Filename}})</code>
+        {{end}}
+        <button type="button" class="btn-insert" data-ref="{{if isVideo .MimeType}}![{{.OriginalName}}](/uploads/{{.Filename}}){{else if isAudio .MimeType}}[{{.OriginalName}}](/uploads/{{.Filename}}){{else}}![{{.OriginalName}}](/uploads/{{.Filename}}){{end}}">↩ einfügen</button>
+      </div>
       {{end}}
     </div>
     {{end}}
-    <input type="file" name="images" multiple accept="image/*" id="image-input">
-    <div id="image-preview" class="image-preview"></div>
     <button type="submit">Speichern</button>
   </form>
 </main>
@@ -40,6 +53,7 @@
 
 {{define "scripts"}}
 <script src="/static/day.js"></script>
+<script src="/static/editor.js"></script>
 {{end}}
 
 {{template "base" .}}