feat: Add new agents and skills for Docker, TestLink, and OpenWrt

- Introduced "Docker Build & Test Engineer" agent for building and testing Docker images.
- Added "TestLink Autotest Engineer" agent for generating and verifying autotests from TestLink cases.
- Created "Branch Review Engineer" agent for reviewing branch diffs and proposing improvements.
- Developed "OpenWrt VPN & Network Engineer" agent for designing and implementing OpenWrt networking with VPN.
- Established a structured directory for agents, skills, prompts, instructions, and hooks under `.github/`.
- Implemented detailed skills for branch review processes, including reading code, analyzing improvements, and applying changes.
- Added skills for OpenWrt network discovery, VPN routing, and hardening.
- Created README files for better documentation and navigation of the repository structure.

.github/instructions/README.md

@@ -0,0 +1,17 @@
+# Instructions
+
+Put shared behavior rules here as `*.instructions.md` files.
+
+## Recommended Patterns
+
+- Global workspace guidance:
+  - `.github/instructions/workspace.instructions.md`
+- File-scoped rules (with `applyTo`):
+  - `.github/instructions/python.instructions.md`
+  - `.github/instructions/tests.instructions.md`
+
+## Notes
+
+- Keep instructions concise and specific.
+- Use `description` and `applyTo` to avoid loading irrelevant context.
+- Do not put multi-step workflows here; use skills for that.