feat: migrate plugin sources to pluginpack 0.11

[steve-calvert-glean]

Summary

• move canonical plugin content under shared/<plugin>/
• consolidate target-specific plugin and repository-root content under overrides/<target>/
• colocate the local MCP implementation, configuration, tests, and shipping manifest under shared/glean/mcp/
• update build, release, and CI paths for the new layout
• upgrade @gleanwork/pluginpack from 0.9.0 to 0.11.0
• preserve the local MCP version-reporting work in its new location

Layout

• plugin overrides: overrides/<target>/<plugin>/
• generated repository-root files: overrides/<target>/root/

Generated output changes

• Claude and Codex MCP implementation files now ship below mcp/
• Claude and Codex MCP command paths point to mcp/start.mjs
• Claude and Cursor generated repositories now include a root LICENSE
• all other generated plugin content remains equivalent

Verification

• clean npm ci using published pluginpack 0.11.0
• npm run check:no-shell
• npm run typecheck:bundle
• 195 MCP tests passed
• Claude, Cursor, and Codex builds completed
• all three generated outputs passed pluginpack validation

Local files

EVAL-CHECKLIST.md and docs/ were intentionally excluded from this PR.