Add v1 contract DB models and migration (#544)

[abhishek-8081]

Closes #544.

Adds the five v1 contract DB models — Input, Extraction, Incident, Form, Report — plus migration 002 and tests. The existing Template, FormSubmission, and Job models are left untouched.

Each model uses a UUID primary key via sa.Uuid() (a real UUID type on Postgres, CHAR(32) on SQLite so the migration tests pass), created_at/updated_at timestamps, and the status enums from #543. The IncidentContract superset lives as a single JSON blob on Extraction rather than separate tables, matching the contract structure. Added an InputType (voice/text) enum to enums.py — the one enum the contract referenced inline without a named entry.

Two deliberate decisions worth flagging for review:

• Job FK: Form.job_id and Report.job_id are plain UUID columns with no FK constraint. The contract's Job entity is UUID/enum-typed, but the existing Job model (from the async work) is int-PK and celery-shaped, so a real FK isn't possible yet. The columns exist with the right type and name so the route layer can use them; a follow-up adds the constraint once the contract Job is resolved. Form.incident_id does get a proper FK to incidents.

• JSON vs JSONB: all JSON columns use sa.JSON (Postgres json, not jsonb) for consistency with migration 001 and SQLite test compatibility. If we later need containment operators or GIN indexing on the blobs — especially incident_contract — a follow-up can switch via with_variant().

Migration 002 was autogenerated then hand-checked; downgrade() drops tables in reverse dependency order. The new models are registered in alembic/env.py and conftest.py so autogenerate and the test harness pick them up.

Tests: 112 passing. test_migrations.py asserts the table/column sets and FK constraints (including that job_id has no FK); test_v1_models.py adds direct ORM round-trip tests covering JSON fields, soft-delete, all 20 form types, and enum status persistence.