Harden API security: input validation, safe auth extraction, new tests, and deploy config

Comprehensive security hardening from audit findings:
- Add validation tags to all DTO request structs (max lengths, ranges, enums)
- Replace unsafe type assertions with MustGetAuthUser helper across all handlers
- Remove query-param token auth from admin middleware (prevents URL token leakage)
- Add request validation calls in handlers that were missing c.Validate()
- Remove goroutines in handlers (timezone update now synchronous)
- Add sanitize middleware and path traversal protection (path_utils)
- Stop resetting admin passwords on migration restart
- Warn on well-known default SECRET_KEY
- Add ~30 new test files covering security regressions, auth safety, repos, and services
- Add deploy/ config, audit digests, and AUDIT_FINDINGS documentation

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

deploy/.gitignore

@@ -0,0 +1,18 @@
+# Local deploy inputs (copy from *.example files)
+cluster.env
+registry.env
+prod.env
+
+# Local secret material
+secrets/*.txt
+secrets/*.p8
+
+# Keep templates and docs tracked
+!*.example
+!README.md
+!shit_deploy_cant_do.md
+!swarm-stack.prod.yml
+!scripts/
+!scripts/**
+!secrets/*.example
+!secrets/README.md