fix(database): B-1 schema integrity and migration fixes

- Fix migration 024 self-insert and bad column reference (F-B1-1, F-B1-2)
  Uses existing enabled/auto_run columns instead of non-existent deprecated
- Abort server on migration failure instead of warning (F-B1-11)
  main.go now calls log.Fatalf, prints [INFO] only on success
- Fix migration 018 scanner_config filename suffix (F-B1-3)
  Renumbered to 027 with .up.sql suffix
- Remove GRANT to non-existent role in scanner_config (F-B1-4)
- Resolve duplicate migration numbers 009 and 012 (F-B1-13)
  Renamed to 009b and 012b for unique lexical sorting
- Add IF NOT EXISTS to all non-idempotent migrations (F-B1-15)
  Fixed: 011, 012, 017, 023, 023a
- Replace N+1 dashboard stats loop with GetAllUpdateStats (F-B1-6)
  Single aggregate query replaces per-agent loop
- Add composite index on agent_commands(status, sent_at) (F-B1-5)
  New migration 028 with partial index for timeout service
- Add background refresh token cleanup goroutine (F-B1-10)
  24-hour ticker calls CleanupExpiredTokens
- ETHOS log format in migration runner (no emojis)

All 55 tests pass (41 server + 14 agent). No regressions.
See docs/B1_Fix_Implementation.md and DEV-025 through DEV-028.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

aggregator-server/internal/database/migrations/023a_command_deduplication.up.sql

@@ -2,13 +2,13 @@
 -- Prevents multiple pending scan commands per subsystem per agent
 
 -- Add unique constraint to enforce single pending command per subsystem
-CREATE UNIQUE INDEX idx_agent_pending_subsystem
+CREATE UNIQUE INDEX IF NOT EXISTS idx_agent_pending_subsystem
 ON agent_commands(agent_id, command_type, status)
 WHERE status = 'pending';
 
 -- Add idempotency key support for retry scenarios
-ALTER TABLE agent_commands ADD COLUMN idempotency_key VARCHAR(64) UNIQUE NULL;
-CREATE INDEX idx_agent_commands_idempotency_key ON agent_commands(idempotency_key);
+ALTER TABLE agent_commands ADD COLUMN IF NOT EXISTS idempotency_key VARCHAR(64) UNIQUE NULL;
+CREATE INDEX IF NOT EXISTS idx_agent_commands_idempotency_key ON agent_commands(idempotency_key);
 
 -- Comments for documentation
 COMMENT ON TABLE agent_commands IS 'Commands sent to agents for execution';