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/server/server_test.go

@@ -376,7 +376,7 @@ func TestSetAndGetRoles(t *testing.T) {
 
 	// Set roles.
 	rr := doRequest(t, handler, "PUT", "/v1/accounts/"+target.UUID+"/roles", map[string][]string{
-		"roles": {"reader", "writer"},
+		"roles": {"admin", "user"},
 	}, adminToken)
 	if rr.Code != http.StatusNoContent {
 		t.Errorf("set roles status = %d, want 204; body: %s", rr.Code, rr.Body.String())