feat(extract): extract call-form event.listen registrations (events v2)

[v0ropaev]

What

The events extractor now also extracts module-level SQLAlchemy event.listen(Target, "event", fn) statements — the v1 KNOWN GAP — as a new registration family sqlalchemy_listen.

• fn must resolve to a first-party top-level function (same module, or imported — reusing the calls.py import-table machinery, lifted to module level with thin class delegates, the _caller_scan_root precedent). Precision-first: unresolvable fn (lambda / attribute / non-first-party) is skipped, never guessed.
• The registration attaches to the handler's artifact (event:{fn_fq}) — which may live in another module than the listen() call — and the artifact gains a grounding edge on the registering file's module span (new role registration_site). Wiring in a third module grounds one artifact across three files: handler + target class + registration site.
• Only module-level calls are extracted (they run deterministically at import time → the claim honestly holds at confidence 1.0). listen(...) inside a function/class body, lambda listeners, and the bare from sqlalchemy.event import listen form are documented gaps.
• Registrations gained form/registration_module/registration_line; call-form registrations sort before merging so full and incremental indexing stay byte-identical.

Version bump

events extractor_version 1 → 2: all event_handler ids recompute on the next index (idempotent re-index; orphaned rows go to the deferred GC); kb describe regenerates event-handler descriptions on its next run. Purely-decorator handlers keep semantically identical payloads. Identity rules in kb.ids untouched.

Gate

Tier-1 events oracle: the call-form known-gap test inverts into a positive test; EXPECTED_EVENTS gains two sqlalchemy_listen tuples; new tests: three-file provenance (hooks.py + db.py + wiring.py), function-body listen gap, lambda-listener gap (9 → 12 tests). Headline HARD gates stay fifteen.

Local: ruff clean, mypy --strict clean, pytest -q → 115 passed, 1 skipped.