docs: add production readiness checklist for extension launch

[skid-dev]

Motivation

• Add a concrete, actionable production-readiness checklist to capture high-impact work required before publishing the Chrome extension.
• The repository currently uses broad host and web-accessible permissions, has incomplete metadata and limited CI/test coverage, so a focused backlog will help prioritize security and release blockers.
• Provide a recommended implementation order so critical issues (permissions, privacy, and robustness) are fixed before feature polish and store packaging.

Description

• Add a new PRODUCTION_TODO.md file containing a detailed checklist covering permissions/privacy, identity/release metadata, reliability/robustness, performance/UX, engineering quality gates, product features to add, and documentation/support.
• The checklist calls out concrete items such as replacing <all_urls> host permissions, scoping web-accessible resources, adding a Privacy Policy and data-retention controls, runtime settings validation and migration, CI lint/test gates, and UX/onboarding features.
• The file also includes a suggested implementation order to prioritize fixes for a safe Chrome Web Store release.

Testing

• Ran a production build with bun run build and the webpack build completed successfully (assets emitted and compilation succeeded).

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Codex Task