trusted proxy, TOTP replay protection, new tests

- Trusted proxy config option for proxy-aware IP extraction
  used by rate limiting and audit logs; validates proxy IP
  before trusting X-Forwarded-For / X-Real-IP headers
- TOTP replay protection via counter-based validation to
  reject reused codes within the same time step (±30s)
- RateLimit middleware updated to extract client IP from
  proxy headers without IP spoofing risk
- New tests for ClientIP proxy logic (spoofed headers,
  fallback) and extended rate-limit proxy coverage
- HTMX error banner script integrated into web UI base
- .gitignore updated for mciasdb build artifact

Security: resolves CRIT-01 (TOTP replay attack) and
DEF-03 (proxy-unaware rate limiting); gRPC TOTP
enrollment aligned with REST via StorePendingTOTP

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/db/migrate.go

@@ -22,7 +22,7 @@ var migrationsFS embed.FS
 // LatestSchemaVersion is the highest migration version defined in the
 // migrations/ directory.  Update this constant whenever a new migration file
 // is added.
-const LatestSchemaVersion = 6
+const LatestSchemaVersion = 7
 
 // newMigrate constructs a migrate.Migrate instance backed by the embedded SQL
 // files.  It opens a dedicated *sql.DB using the same DSN as the main