Add client-side note encryption

- WebCrypto keyring (PBKDF2 600k + AES-GCM master key) and per-note/per-image keys
- Encrypt/decrypt commands convert the note and its own images, deleting the originals
- Unlock, setup and change-password dialogs; manual lock; lock on page close
- Encrypted images are decrypted to blob URLs; pasted images are encrypted before upload
- Rewrite image links in the browser when renaming an encrypted note
- Skip local drafts for encrypted notes and confirm before closing with unsaved changes
- Show encrypted notes as locked with an explanation outside secure contexts

web/src/app/Icon.vue

@@ -14,6 +14,7 @@ const paths = {
   restore: 'M3 12a9 9 0 1 0 3-6.7L3 8M3 3v5h5',
   edit: 'M12 20h9M16.5 3.5a2.1 2.1 0 0 1 3 3L7 19l-4 1 1-4z',
   search: 'M11 18a7 7 0 1 0 0-14 7 7 0 0 0 0 14zM21 21l-4.35-4.35',
+  lock: 'M5 11h14v10H5zM8 11V7a4 4 0 0 1 8 0v4',
   command: 'M18 3a3 3 0 0 0-3 3v12a3 3 0 1 0 3-3H6a3 3 0 1 0 3 3V6a3 3 0 1 0-3 3h12a3 3 0 0 0 0-6z',
 }
 defineProps<{ name: keyof typeof paths; size?: number }>()