feat(proceeding-type): explicit ערר/בל"מ field for cases + corpus

Same case_number can exist as both a regular appeal (ערר) and an
extension-of-time request (בל"מ), and we were inferring the difference
from appeal_subtype prefixes — fragile, and case-number lookups
weren't disambiguated. Now stored as a first-class field on both
case_law (corpus) and cases (live cases), with partial unique indexes
on (case_number, proceeding_type).

- SCHEMA_V15: column + CHECK constraints + backfill from
  appeal_subtype LIKE 'extension_request_%' + partial unique indexes
  replace the old global UNIQUE(case_number).
- derive_proceeding_type() centralizes the inference rule
  (extension_request_* → בל"מ; subject regex fallback; default ערר).
- Metadata extractor prompt asks Claude to populate the new field
  explicitly; apply_to_record writes it for internal_committee rows.
- internal_decision_upload, case_create, case_update accept an
  optional proceeding_type; FastAPI request models expose it.
- Wizard + edit dialog get a sided Select; case header renders the
  resolved label (ערר / בל"מ).
- Uploaded the 2 staged בל"מ decisions on betterment levy:
  8126/24 (סופר נוח, 13 chunks), 8047/23 (הרנון, 48 chunks).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/app.py

@@ -1234,6 +1234,9 @@ class CaseCreateRequest(BaseModel):
     # send a domain value explicitly.
     practice_area: str = ""
     appeal_subtype: str = ""
+    # proceeding_type: 'ערר' / 'בל"מ'. Empty → auto-derived from
+    # appeal_subtype / subject downstream.
+    proceeding_type: str = ""
 
 
 class CaseUpdateRequest(BaseModel):
@@ -1249,6 +1252,7 @@ class CaseUpdateRequest(BaseModel):
     respondents: list[str] | None = None
     property_address: str = ""
     permit_number: str = ""
+    proceeding_type: str = ""
 
 
 @app.post("/api/cases/create")
@@ -1268,6 +1272,7 @@ async def api_case_create(req: CaseCreateRequest):
         expected_outcome=req.expected_outcome,
         practice_area=req.practice_area,
         appeal_subtype=req.appeal_subtype,
+        proceeding_type=req.proceeding_type,
     )
     parsed = json.loads(result)
 
@@ -1399,6 +1404,7 @@ async def api_case_update(case_number: str, req: CaseUpdateRequest, background_t
             respondents=req.respondents,
             property_address=req.property_address,
             permit_number=req.permit_number,
+            proceeding_type=req.proceeding_type,
         )
     except ValueError as exc:
         raise HTTPException(422, str(exc))