fix(corpus): committee decisions are persuasive, never binding (INV-DM7)

ועדת-ערר decisions (source_kind=internal_committee / source_type=
appeals_committee) are persuasive authority — they do not bind another
committee, nor the committee itself. The stored is_binding column wrongly
defaulted to True across the FastAPI form + service/db layers, so 46 of 92
committee rows were marked binding and got the BINDING halacha-extraction
prompt. Authority is structural for this source (INV-DM7) — normalize at the
source (G1), not trust the input.

Changes:
- db.create_internal_committee_decision: coerce is_binding=False (structural)
- db.create_external_case_law: coerce False when source_type=appeals_committee
- db.update_case_law: coerce False when a patch relabels source_type=
  appeals_committee (Gemini reclassification path)
- internal_decisions.migrate_from_external_corpus: set is_binding=FALSE on
  the external→internal reclassification UPDATE
- service + FastAPI-form defaults: True → False for the internal path
- SCHEMA_V42: backfill legacy committee rows (is_binding True→False) +
  CHECK constraint case_law_committee_not_binding_check so a binding
  committee row can never be written again ("so it doesn't recur")
- spec: X8-field-provenance aligned to INV-DM7

Verified against live DB in a rollback transaction: 46 rows flip to 0;
court_ruling (239) + cited_only (31) unaffected; binding-committee INSERT
rejected by the constraint.

Invariants: INV-DM7 (authority ⊥ rule-type) · G1 (normalize at source) ·
G2 (single source of truth, no parallel path).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/spec/X8-field-provenance.md

@@ -35,14 +35,14 @@
 | `case_number` (citation) | CHAIR (חובה) | מפתח idempotency |
 | `full_text`, `extraction_status`, `source_kind` | DETERMINISTIC | — |
 | `case_name`, `court`, `date`, `headnote`, `summary`, `key_quote`, `subject_tags`, `appeal_subtype`, `precedent_level`, `source_type`, `citation_formatted` | CHAIR או OPUS | Opus ממלא רק אם ריק |
-| `is_binding` | CHAIR (default true) | קובע prompt-הלכה |
+| `is_binding` | CHAIR (default true) **אך** DETERMINISTIC-false ל-`source_type=appeals_committee` | קובע prompt-הלכה. סמכות מבנית ([INV-DM7](02-data-model.md#inv-dm7-סיווג-הלכה--סמכות-נגזרת--תפקיד-כלל-מסווג-שני-צירים-לא-enum-אחד)): מקור-ועדה הוא תמיד persuasive — נכפה ל-false ב-`create_external_case_law` ונאכף ע"י `case_law_committee_not_binding_check` |
 | chunks (`content`/`section_type`/`page_number`) | DETERMINISTIC | — |
 | `embedding` (chunks) | Voyage (לא-LLM-reasoning) | ⚠ לא-GENERATED ([gap-audit GAP-09](gap-audit.md)) |
 | כל `halachot` | OPUS | נכנס pending_review |
 
 ### 2ב. החלטה פנימית (`case_law`, source_kind=`internal_committee`)
 כמו 2א, ובנוסף: `case_number` **חובה**; `chair_name`/`district`/`proceeding_type` — CHAIR או OPUS או DERIVED;
-`source_type` = `appeals_committee` (DETERMINISTIC קבוע). placeholder `"(טרם חולץ)"` מסומן ל-chair_name/district
+`source_type` = `appeals_committee` (DETERMINISTIC קבוע); `is_binding` = `false` (DETERMINISTIC קבוע — נכפה ב-`create_internal_committee_decision`, [INV-DM7](02-data-model.md#inv-dm7-סיווג-הלכה--סמכות-נגזרת--תפקיד-כלל-מסווג-שני-צירים-לא-enum-אחד): החלטת-ועדה אינה מחייבת ועדה אחרת ולא את עצמה — תמיד persuasive). placeholder `"(טרם חולץ)"` מסומן ל-chair_name/district
 ריקים ומטופל כריק ע"י ה-extractor.
 
 ### 2ג. מסמך-תיק (`documents`)