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>

mcp-server/src/legal_mcp/services/practice_area.py

@@ -263,6 +263,18 @@ def is_blam_subtype(appeal_subtype: str) -> bool:
     return appeal_subtype in BLAM_SUBTYPES
 
 
+def derive_proceeding_type(*, appeal_subtype: str = "", subject: str = "") -> str:
+    """Return 'בל"מ' / 'ערר' for appeals-committee decisions/cases.
+
+    Priority: explicit subtype prefix → subject regex → default 'ערר'.
+    """
+    if appeal_subtype and appeal_subtype.startswith("extension_request_"):
+        return 'בל"מ'
+    if subject and is_blam_subject(subject):
+        return 'בל"מ'
+    return "ערר"
+
+
 def derive_domain_practice_area(case_number: str) -> str:
     """Map a case_number prefix to a domain practice_area (axis B).