[codex] Harden live mode helper security

[inbusiness23]

Summary

• require the live-mode session token before serving /live.js
• restrict CORS to the origin that loaded the tokened live script
• keep source reads and explicit helper file paths inside the project root
• cap JSON request bodies and harden copy-edit agent subprocess defaults
• regenerate provider skill copies from the build pipeline

Why

A security review found that live mode treated localhost as the trust boundary. Any unrelated local page or process could load /live.js, wildcard CORS allowed broad cross-origin access, /source used a fragile prefix check, JSON bodies were unbounded, and copy-edit subprocesses defaulted to permission-bypass flags with the full environment. This PR tightens those local live-mode boundaries while preserving the existing workflow.

Validation

• bun install --frozen-lockfile
• npm run build
• node --check skill/scripts/live-server.mjs skill/scripts/live-inject.mjs skill/scripts/live-copy-edit-agent.mjs skill/scripts/live-wrap.mjs skill/scripts/live-insert.mjs skill/scripts/live-browser.js
• node --test tests/live-server.test.mjs tests/live-inject.test.mjs tests/live-insert.test.mjs tests/live-wrap.test.mjs tests/live-copy-edit-agent.test.mjs tests/framework-fixtures.test.mjs
• git diff --check