feat: MVP-5 Sprint 4 - External Capture via Bookmarklet

- Add bookmarklet for capturing web content from any page
- Add capture confirmation page with edit before save
- Add secure /api/capture endpoint with rate limiting
- Add bookmarklet instructions component with drag-and-drop

src/lib/external-capture.ts

@@ -0,0 +1,25 @@
+export interface CapturePayload {
+  title: string
+  url: string
+  selection: string
+}
+
+export function encodeCapturePayload(payload: CapturePayload): string {
+  const params = new URLSearchParams({
+    title: payload.title,
+    url: payload.url,
+    selection: payload.selection,
+  })
+  return params.toString()
+}
+
+export function generateBookmarklet(): string {
+  const code = `
+    var title = document.title;
+    var url = location.href;
+    var selection = window.getSelection().toString();
+    var params = new URLSearchParams({title, url, selection});
+    window.open('/capture?' + params.toString(), '_blank');
+  `.replace(/\s+/g, ' ').trim()
+  return `javascript:${code}`
+}