P3-01/02/03: restore wizard backend + templates + restore-shaped job page

End-to-end wizard from /hosts/{id}/restore (or per-snapshot deep link
/hosts/{id}/snapshots/{sid}/restore) → tree-browse → dispatch →
restore-shaped live job page.

Backend (internal/server/http/ui_restore.go):
- GET handlers render the four-step wizard against the wireframe shape
  in docs/superpowers/specs/2026-05-04-p3-restore-design.md.
- HTMX tree partial endpoint hits fetchTreeWithCache (P3-X2) so each
  directory expansion is a sub-second cached lookup after the first
  miss.
- POST validates: snapshot_id non-empty, ≥1 absolute path, in-place
  mode requires confirm_hostname == host name, agent online. On error
  re-renders the wizard with the operator's input intact. Happy path
  mints a job_id, computes the new-directory target as
  /var/restic-restore/<job-id>/ (operator can't escape the prefix —
  server picks it), creates the job row, ships command.run with
  kind=restore + RestorePayload, writes a host.restore audit row,
  returns HX-Redirect (or 303) to the live job page.

Templates:
- host_restore.html: single-page progressively-enabled wizard matching
  _diag/p3-restore-wizard wireframe. Form-state-driven JS computes a
  running tally of selected paths and the step-4 confirm summary
  client-side; the server re-renders on validation failure with form
  fields preserved.
- partials/tree_node.html: recursive HTMX-served tree fragment.
- Top-level Restore button on host_detail right rail + per-snapshot
  Restore action on snapshot rows replace the previous P3-stub.

Restore-shaped job page (job_detail.html):
- Progress widget rendered as a panel rather than a bare strip when
  the job is active.
- Current-file display under the bar, updated from log.stream stdout
  lines that look like absolute paths. Hidden for non-restore kinds.

Migration 0012:
- Add restore + diff to the jobs.kind CHECK. Rebuild required (SQLite
  can't ALTER CHECK in place); follows the safe pattern from 0005.
  Defensive: stash job_logs into a temp table before the rebuild and
  INSERT OR IGNORE back afterwards so even if SQLite cascades on
  DROP TABLE jobs the log history survives.

Tests:
- ui_restore_test covers GET step-1 render, GET pre-selected snapshot
  summary card, POST missing snapshot, POST missing paths, POST
  in-place wrong-hostname rejection (no command.run leaks to the
  agent), POST happy path (HX-Redirect + correct payload + audit
  row), POST against offline host returns 503.

Restage block (CLAUDE.md) deferred to the end of the restore phase.

internal/server/ui/ui.go

@@ -92,6 +92,7 @@ func New() (*Renderer, error) {
 		"templates/partials/toast.html",
 		"templates/partials/awaiting_agent.html",
 		"templates/partials/host_chrome.html",
+		"templates/partials/tree_node.html",
 	}
 
 	pageEntries, err := fs.Glob(web.FS, "templates/pages/*.html")