feat: sync guards + import restore mode + inline progress + uncategorised polish

Sync engine
- Cross-account guard: refuse to merge a remote snapshot whose
  username differs from the currently-signed-in one (confirm dialog,
  Cancel by default) so a shared WebDAV URL / same sync password
  between accounts stops silently mixing vaults.
- Local tombstones veto: skip any remote entry whose uuid is already
  in the local entry_tombstones table — otherwise a perm-delete on
  this device was getting undone on the next pull.
- "deleted" counter fixed: report only tombstones that actually
  removed a live local entry this round, not the accumulated history
  the toast used to inflate ("73 deleted" for 48 real deletes).
- Push failure surfaces syncStatus reset + toast so state doesn't
  get stuck on a stale phase label.

Sync progress feedback
- Inline #syncStatus label next to the Sync button reports each
  phase: Local backup… → Pulling… → Merging… → Preparing… N/total
  (per-entry counter during the slow buildSyncSnapshot decrypt loop)
  → Encrypting… → Pushing…, then clears.
- Sync now / Test connection buttons are disabled while any run is
  in flight so double-clicks can't kick off a concurrent sync.

Import (JSON only — CSV out of scope)
- Uuid-aware dedup: split parsed rows into fresh (new uuid) vs
  overlaps (uuid already present locally).
- Overlaps prompt: confirm dialog offers Overwrite (restore/roll
  back) or Skip. Overwrite PUTs the file's payload over each match;
  Skip drops them and only imports fresh. Prevents the "re-import
  doubles everything" regression while still allowing restore.
- Bulk-import call is skipped entirely when there's nothing fresh to
  send (avoids a POST with an empty entries array).
- Template notes with empty body but populated custom_fields
  (credit-card, ssh-key, etc.) no longer skipped as "note body
  required" — kept as long as at least one custom field has a value.

Sidebar / uncategorised view
- "(no folder)" pseudo-entry stays visible whenever the vault has
  any real folder, so it always works as a drag target for
  uncategorising — and doesn't vanish mid-action when the user is
  currently viewing it.
- Header title reads "(no folder)" for state.view === 'folder:All'
  instead of the ambiguous "All".
- Dedicated empty-state copy for the uncategorised view.

Rebuild assets required.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

index.html

@@ -707,6 +707,7 @@
                     <div style="display:flex;gap:6px;flex-wrap:wrap;align-items:center;margin-top:6px">
                         <button class="btn btn-ghost btn-sm" id="syncTestBtn">Test connection</button>
                         <button class="btn btn-primary btn-sm" id="syncNowBtn">Sync now</button>
+                        <span id="syncStatus" style="font-size:11px;color:var(--accent);display:none"></span>
                         <span id="syncLast" style="font-size:11px;color:var(--text-faint)"></span>
                     </div>
                 </div>