refactor(repo): consolidate openflare-server to root and move subprojects to internal/apps

- Merge all files inside openflare-server to the repository root directory.
- Relocate agent, relay, and flared subprojects from internal/ to internal/apps/.
- Combine docker-compose files and update build context paths to root.
- Update GitHub workflows and Dockerfiles to refer to new directories and package names.
- Rewrite Go package imports across all files.
- Resolve database renew test race condition and clean up docs.

pkg/cap/errs.go

@@ -0,0 +1,15 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package cap
+
+const (
+	errInvalidTokenFormat = "invalid token format"
+	errInvalidHeader      = "invalid header"
+	errSignatureMismatch  = "signature mismatch"
+	errInvalidToken       = "invalid_token"
+	errScopeMismatch      = "scope_mismatch"
+	errExpired            = "expired"
+	errInvalidSolutions   = "invalid_solutions"
+	errInvalidSolution    = "invalid_solution"
+)