Task: B3: Teach load_org_model() to parse table-only sections

load_org_model() produces a domain_entity model dict that includes all fields previously only available via load_org_table_model(): validation_fn, insert_trigger.validations, has_tenant_id, coding_scheme, image_id. The table loader is not deleted yet.

• load_org_model() parses #+has_tenant_id, #+coding_scheme, #+image_id from frontmatter
• load_org_model() parses * Validation function section into domain_entity.validation_fn
• load_org_model() parses * Insert trigger / ** Validations org table into domain_entity.insert_trigger.validations
• Existing entity org files that lack these sections produce identical output to before (no regression)

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

Shipped in one commit on feature/codegen-unification-blockers.

Extended org_document_to_model() in codegen/org_loader.py with five new parse paths:

• Frontmatter scalars (after the existing string-key loop):
  • #+has_tenant_id → de["has_tenant_id"] (bool via _parse_typed)
  • #+coding_scheme → de["coding_scheme"] (raw string; boolean flags computed at render time)
  • #+image_id → de["image_id"] (bool via _parse_typed)
• Sections (after the * SQL block):
  • * Validation function property drawer → de["validation_fn"] dict; default / default_value keys kept as raw strings for Mustache 0-falsy guard
  • * Insert trigger / ** Validations org table → de["insert_trigger"]["validations"] list of row dicts

load_org_table_model() is unchanged; it continues to produce {"table": {...}} as before. All existing entity org files that lack these sections produce identical output (9 smoke tests cover all paths including backward-compat, and 0 component-scaffold regression failures).

Acceptance met:

• load_org_model() parses #+has_tenant_id, #+coding_scheme, #+image_id from frontmatter. ✓
• load_org_model() parses * Validation function into domain_entity.validation_fn. ✓
• load_org_model() parses * Insert trigger / ** Validations into domain_entity.insert_trigger.validations. ✓
• Existing entity org files without these sections produce identical output. ✓