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/static/editor.js

@@ -0,0 +1,84 @@
+"use strict";
+(function () {
+    'use strict';
+    function initEditor(ta) {
+        var _a, _b;
+        async function upload(file) {
+            var _a;
+            const form = new FormData();
+            form.append('file', file);
+            const statusEl = (_a = ta.parentElement) === null || _a === void 0 ? void 0 : _a.querySelector('.upload-status');
+            if (statusEl)
+                statusEl.textContent = '↑ ' + file.name + ' …';
+            try {
+                const res = await fetch('/media', { method: 'POST', body: form });
+                if (!res.ok) {
+                    if (statusEl)
+                        statusEl.textContent = '✗ Fehler beim Hochladen';
+                    return;
+                }
+                const data = await res.json();
+                insertAtCursor('\n' + data.ref + '\n');
+                if (statusEl)
+                    statusEl.textContent = '';
+            }
+            catch (_e) {
+                if (statusEl)
+                    statusEl.textContent = '✗ Fehler beim Hochladen';
+            }
+        }
+        function insertAtCursor(text) {
+            const start = ta.selectionStart;
+            ta.value = ta.value.slice(0, start) + text + ta.value.slice(ta.selectionEnd);
+            ta.selectionStart = ta.selectionEnd = start + text.length;
+            ta.focus();
+        }
+        // Paste: catch file pastes
+        ta.addEventListener('paste', function (e) {
+            var _a;
+            const items = (_a = e.clipboardData) === null || _a === void 0 ? void 0 : _a.items;
+            if (!items)
+                return;
+            for (let i = 0; i < items.length; i++) {
+                if (items[i].kind === 'file') {
+                    e.preventDefault();
+                    const file = items[i].getAsFile();
+                    if (file)
+                        void upload(file);
+                    return;
+                }
+            }
+        });
+        // Drag & Drop onto textarea
+        ta.addEventListener('dragover', function (e) {
+            e.preventDefault();
+            ta.classList.add('drag-over');
+        });
+        ta.addEventListener('dragleave', function () {
+            ta.classList.remove('drag-over');
+        });
+        ta.addEventListener('drop', function (e) {
+            var _a;
+            e.preventDefault();
+            ta.classList.remove('drag-over');
+            const files = (_a = e.dataTransfer) === null || _a === void 0 ? void 0 : _a.files;
+            if (!files)
+                return;
+            for (let i = 0; i < files.length; i++)
+                void upload(files[i]);
+        });
+        // File picker button
+        const picker = (_a = ta.parentElement) === null || _a === void 0 ? void 0 : _a.querySelector('.media-picker');
+        const input = (_b = ta.parentElement) === null || _b === void 0 ? void 0 : _b.querySelector('.media-file-input');
+        if (picker && input) {
+            picker.addEventListener('click', function () { input.click(); });
+            input.addEventListener('change', function () {
+                if (!input.files)
+                    return;
+                Array.from(input.files).forEach(f => void upload(f));
+                input.value = '';
+            });
+        }
+    }
+    document.querySelectorAll('textarea[name="description"]').forEach(initEditor);
+})();