fix: PR8.1 — status healthy init + object_units rebuild + version bump

- status.py: healthy=True init before if exists: (was UnboundLocalError
  when vector DB doesn't exist)
- manifest.py: RETRIEVAL_POLICY_VERSION l4.body.v1 → l4.body.v2 to
  trigger object_units rebuild with PR7 fix (unit_id fallback)
- Object_units corrected from 20→311 after rebuild (was INSERT OR
  REPLACE overwrite from old empty unit_id)
- Coverage parity: 20 papers have body_units = 20 have object_units ✅
  (body=811 chunks, object=311 chunks, expected difference due to
   section-split vs 1:1 caption structure)
- Unit tests: 97 pass (subset)

paperforge/embedding/status.py

@@ -48,6 +48,7 @@ def get_embed_status(vault: Path) -> dict:
     body_chunk_count = 0
     error = ""
     corrupted = False
+    healthy = True
     if exists:
         # Count paperforge_fulltext
         try:

paperforge/retrieval/manifest.py

@@ -12,7 +12,7 @@ from hashlib import sha256
 from typing import Any
 import json
 
-RETRIEVAL_POLICY_VERSION = "l4.body.v1"
+RETRIEVAL_POLICY_VERSION = "l4.body.v2"
 
 
 def compute_body_units_hash(units: list[dict]) -> str: