feat(ha-entity-snapshots): consume restoration indicator in the catch-up receive handler (task 6.1)

ha_handle_snapshot_chunk now logs whether a received checkpoint was
fully entity-restored or was a legacy position-only file (INFO level,
framed as an expected rollout state -- never an error, per design.md).
The rc-gates-applied_lsn control flow is byte-for-byte unchanged from
task 5.2 (confirmed by review) -- this task is purely additive
observability, matching design.md's own note that this call site
"needs no change" once persist_load_snapshot's gate is correct.

New test drives the legacy path end-to-end through the real production
handler (rc==0, file renamed, applied_lsn advances to the legacy LSN).

This completes the integration layer -- write path (jobs+queues),
restore-before-advance read path, and the production wiring are all in
place and independently reviewed. Only validation tasks remain (7.1
chaotic soak, 8.1 rollback compatibility).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JDYFbrgyDHbvNYcxApKhrX

.kiro/specs/ha-entity-snapshots/tasks.md

@@ -92,8 +92,8 @@
   - _Requirements: 2.1, 2.2, 2.3, 2.4, 5.1, 5.2_
   - _Boundary: Persistence Layer (load_snapshot)_
 
-- [ ] 6. Integration: wire the catch-up receive path to the new restore contract
-- [ ] 6.1 Consume the new restoration indicator in the snapshot-chunk receive handler
+- [x] 6. Integration: wire the catch-up receive path to the new restore contract
+- [x] 6.1 Consume the new restoration indicator in the snapshot-chunk receive handler
   - The handler advances the member's applied position only after the load succeeds (unchanged
     ordering); on a legacy (position-only) file it logs the fallback rather than treating it as
     a failure