[Plugin] next-dev: switch to plugin-level hooks + add test server
- Move hooks from SKILL.md frontmatter to hooks/hooks.json. Skill-scoped
hooks are not reliably supported by Claude Code (anthropics/claude-code#17688);
the plugin-level hooks gate on .claude/port for the same activation semantics.
- Self-disable when the dev server is unreachable: hooks delete .claude/port
so a stale port file from a previous session doesn't burn the timeout
every turn.
- Make dismiss-errors.mjs an unconditional escape hatch (drops the
node_modules/turbopack-stub heuristics).
- Add a fake MCP server (test/start-test-server.mjs) plus testing guide for
exercising the full hook flow without a real Next.js dev server.
- Drive-by: fix marketplace source paths for both next-dev and cache-components
to include the .claude-plugin/ prefix so they actually resolve.