Task: Fix synthetic entity model drift: update to latest format and regenerate

Mirror Fix refdata entity model drift for ores.synthetic: regenerate every ores.synthetic domain_entity and junction model (compass codegen entity list) against current codegen templates. Where a model uses an outdated format/convention rather than the templates having simply moved on, update the model to the current convention before regenerating. Commit the resulting clean tree.

Along the way, apply the same lessons learned fixing refdata's drift: check whether any entity's SQL/domain/messaging layer is explicitly hand-maintained (a doc comment flagging missing paste-block coverage) before doing a full regen – prefer --address-scoped regen for anything so flagged; grep synthetic generators for hardcoded/fabricated soft-FK values (coding scheme codes, lookup-table codes) that don't match what a freshly-recreated default database actually seeds.

• Every ores.synthetic domain_entity and junction model is regenerated via compass codegen entity generate and shows zero diff on a second regen (idempotent).
• Any model found using an outdated format/convention is updated to the current one before regenerating.
• Any entity whose SQL/domain/messaging layer is hand-maintained (flagged in its own model doc, mirroring party's) is excluded from a full regen and only its safe facets (e.g. Qt) are regenerated, same as party's treatment in the refdata task.
• Synthetic generators for FK-referencing fields are checked against actual seed SQL (the default db recreate chain, not optional artefact/dataset scripts) and fixed if they fabricate values that don't exist there.
• compass build and full rat pass after the regenerated files are committed.
• No entity outside synthetic is touched.

(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.)

Manual QA scenarios (scaffolded via compass add test_scenario, run through the QA Validation Runner panel) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.

All 7 ores.synthetic entities (folder, fx_spot_generation_config, gmm_component, ir_curve_generation_config, ir_curve_template_entry, market_data_generation_config, yield_curve_process_type) had drifted onto a structural convention current codegen no longer recognises: a top-level * Primary key / * Natural keys org heading instead of :primary_key:=/:natural_key:= field flags inside * Columns. None of them could be regenerated at all (validator: "Missing primary key"). Migrated each model's key fields into * Columns (preserving every property, prose, and generator block byte-for-byte otherwise), then regenerated all 7 fully. No entity outside synthetic touched, no hand-maintained-SQL flags found on any of the 7 models.

Regenerating also surfaced a second template gap in cpp_history_field_mapper: its natural_keys branch didn't handle an int natural key (gmm_component.component_index, ir_curve_template_entry.sequence_index) – same class of bug as the date/timestamp gap found fixing refdata's calendar_exception. Added the missing is_int branch.

Because these entities had never successfully regenerated before, several downstream generated layers (messaging registrars, history-field-mappers, a changed-event) didn't exist on disk yet; committing the regen creates them for the first time.

compass build and full rat green after every commit.

Task-ID: 6C67EAF7-B863-42D7-A571-CD6DA82242EC