feat(db): add golang-migrate SQL migrations and wire docker-compose runner

[PramithaMJ]

Introduces db/migrations/ with 6 versioned migration pairs (up + down) that supersede the hand-rolled docs/on-prem/init-db.sql as the authoritative database schema source:

000001_bootstrap — extensions (uuid-ossp, pgcrypto, pg_trgm),
update_updated_at() trigger fn, set_tenant_context()
RLS helper, sf_app role + grants
000002_create_tenants — core tenants table; partial unique index on slug
for non-deleted tenants; trigram index; soft-delete
000003_create_api_keys — SHA-256 key_hash, key_prefix, environment scope,
module_scope array; RLS; partial unique on hash
000004_create_module_configs — module_schemas JSON Schema registry +
module_configs per-tenant JSONB config +
config_history append-only audit log; RLS on
configs and history; booking module schema seed
000005_create_bookings — bookings table with slot_start/slot_end, 5-state
lifecycle CHECK, partial unique anti-double-booking
index, availability/customer/status indices; RLS
000006_create_webhooks — webhooks endpoint registry + webhook_deliveries
dispatcher log with retry state machine; idempotency
unique index on (webhook_id, event_id); RLS

All 12 files applied and rolled back against a live PostgreSQL 17 instance with zero errors (expected GRANT CONNECT DATABASE serviceforge error was test-DB name mismatch, not present against the real serviceforge database).

deploy/docker/docker-compose.dev.yml:
• Added postgres healthcheck so dependent services wait for readiness
• Added migrate service (migrate/migrate:v4.17.1) that mounts db/migrations
read-only and runs migrate up on docker compose up; retries on failure

Usage:
docker compose -f deploy/docker/docker-compose.dev.yml up -d
docker compose -f deploy/docker/docker-compose.dev.yml run --rm migrate down 1