feat: add first-class codex plugin directory

[benvinegar]

Summary

• add a first-class codex/ plugin directory
• package Codex plugin as @modemdev/glance-codex
• add Codex release automation (release-codex.yml, tag format codex-v*)
• update Codex README with package install + publish instructions
• update root README plugin table to include the Codex package install command

Details

Packaging

• new codex/package.json with npm metadata, publish files, and bin entry:
  • glance-codex -> servers/glance-mcp.js
• codex/servers/glance-mcp.js now contains a self-contained MCP runtime (no cross-directory runtime import)
• codex/servers/glance-mcp.d.ts exported for typed consumers

Release flow

• added .github/workflows/release-codex.yml
• validates tag/version alignment, npm uniqueness, npm pack --dry-run, and publishes with provenance

Tests/docs

• codex/glance.test.ts now checks package metadata (name, main, bin) in addition to manifest and MCP config
• README updates include packaged install path:
  • codex mcp add glance -- npx -y @modemdev/glance-codex

Validation

• npm test
• npm exec -- tsc --noEmit
• cd codex && npm pack --dry-run