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/README.md

@@ -0,0 +1,35 @@
+# Copilot Customization Architecture
+
+This repository keeps Copilot customizations in a layered structure under `.github/`.
+
+## Directory Map
+
+- `agents/` - custom agent definitions (`*.agent.md`)
+- `instructions/` - always-on or file-scoped behavior rules (`*.instructions.md`)
+- `prompts/` - reusable one-shot commands (`*.prompt.md`)
+- `hooks/` - deterministic lifecycle hooks (`*.json`)
+- `skills/` - canonical skill directories (`<skill-name>/SKILL.md`)
+
+## Canonical Storage Rules
+
+1. Agent definition lives at:
+   - `.github/agents/<agent-name>.agent.md`
+2. Skill source lives in:
+   - `.github/skills/<skill-name>/SKILL.md`
+4. Prompt files live in `.github/prompts/*.prompt.md`.
+5. Instruction files live in `.github/instructions/*.instructions.md`.
+6. Hook files live in `.github/hooks/*.json`.
+
+## Why This Layout
+
+- Keeps a flat, standard layout used in most repositories.
+- Simplifies navigation: agents in one place, skills in one place.
+- Separates deterministic automation (`hooks`) from advisory instructions.
+- Keeps agent and skill lifecycles independent.
+
+## Change Policy
+
+- Keep only `.agent.md` files under `.github/agents/`.
+- Keep only skill folders under `.github/skills/`.
+- Keep descriptions trigger-rich ("Use when: ...") for discovery.
+- Do not duplicate skill content in multiple places.