feat(qwencode): add mcp, commands, subagents, skills, and hooks adapters

[dyoshikawa]

Summary

Adds five missing feature adapters for the qwencode (Qwen Code) target, which previously supported only rules/ignore/permissions:

• mcp — mcpServers in .qwen/settings.json (project) / ~/.qwen/settings.json (global); stdio/SSE/HTTP transports, per-server includeTools/excludeTools, global mcp.allowed/mcp.excluded. Modeled on the Gemini CLI MCP adapter.
• commands — .qwen/commands/*.md (project) / ~/.qwen/commands/ (global). Markdown with description frontmatter — Qwen has deprecated the TOML command format, so this diverges from Gemini CLI and follows the Markdown command adapters instead.
• subagents — .qwen/agents/*.md (project) / ~/.qwen/agents/ (global), Markdown + YAML frontmatter (name, description, model, approvalMode, tools, disallowedTools, maxTurns, color, mcpServers, hooks).
• skills — .qwen/skills/<name>/SKILL.md (project) / ~/.qwen/skills/ (global) with supporting files; frontmatter name, description, priority, paths, user-invocable, disable-model-invocation.
• hooks — hooks key in .qwen/settings.json. Qwen's event surface differs from Gemini's, so a Qwen-specific QWENCODE_HOOK_EVENTS constant + canonical mapping were added rather than reusing the Gemini set; only canonical HookEvent values with a genuine Qwen equivalent are mapped.

Also flips qwencode to supportsGlobal: true and wires each adapter into its processor, gitignore registry, README / docs/reference/supported-tools.md / docs/reference/file-formats.md (with the skills/rulesync/ mirror synced), and the Tool × Feature e2e happy-path matrices.

Validation evidence (primary sources)

• Commands (Markdown; TOML deprecated): https://github.com/QwenLM/qwen-code/blob/main/docs/users/features/commands.md
• Sub-agents: https://github.com/QwenLM/qwen-code/blob/main/docs/users/features/sub-agents.md
• Skills: https://github.com/QwenLM/qwen-code/blob/main/docs/users/features/skills.md
• MCP: https://github.com/QwenLM/qwen-code/blob/main/docs/users/features/mcp.md
• Hooks: https://github.com/QwenLM/qwen-code/blob/main/docs/users/features/hooks.md

Test plan

pnpm cicheck is fully green: format, oxlint, typecheck, 6546 unit tests / 275 files, skill-docs sync, cspell, secretlint. New co-located unit tests for each of the five adapters plus Qwen Code cases added to the e2e-{mcp,commands,subagents,skills,hooks} matrices.

Closes #1888

[dyoshikawa]

@dyoshikawa Thank you!