docs: adopt doctrine project manifest

[shtse8]

Summary

• adopt the doctrine project manifest, repo-local agent instructions, and project boundary documentation
• add affected CI lanes for manifest/control-plane-only changes in the main package workflow and SWC plugin workflow
• migrate touched workflow jobs to the canonical sylphx-linux-standard runner profile

Scope

This PR intentionally excludes the SWC/Rust/test changes from #4. That branch now mixes manifest adoption with product and baseline CI repair; this branch keeps the control-plane rollout isolated.

Validation

• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/test.yml"); YAML.load_file(".github/workflows/swc-plugin-test.yml")'
• git diff --check
• python3 -m json.tool .doctrine/project.json
• final affected classifier simulation: product_changed=false
• project-control-plane-audit.py --local /Users/kyle/.codex/worktrees/sylphx-silk-control-plane --fail-on-drift --json
• runner-profile-conformance-audit.py --local /Users/kyle/.codex/worktrees/sylphx-silk-control-plane --fail-on-drift --json