feat: byot.

[knightedcodemonkey]

First step at #18

[Copilot]

Pull request overview

This PR adds the first slice of the BYOT (Bring Your Own Token) groundwork for the planned AI side panel feature (#18): a feature-flagged UI for entering a GitHub PAT, persisting it locally, and using it to list writable repositories via the GitHub API.

Changes:

• Adds a feature flag (?feature-ai=true / localStorage) to show/hide BYOT controls.
• Implements PAT storage/masking + GitHub API repo discovery and selection persistence.
• Adds Playwright coverage and a BYOT setup guide in docs.

Reviewed changes

Copilot reviewed 11 out of 13 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/styles/ai-controls.css	Adds styling for the BYOT controls (token input/buttons + repo select).
src/styles.css	Imports the new AI/BYOT controls stylesheet.
src/modules/github-token-store.js	localStorage-backed token load/save/clear + masking helper.
src/modules/github-byot-controls.js	BYOT UI controller: token validation via repo listing, repo selection persistence.
src/modules/github-api.js	GitHub API client to list writable repositories (pagination + normalization).
src/modules/feature-flags.js	Feature flag for enabling the AI/BYOT UI via query param/localStorage.
src/index.html	Adds the BYOT controls markup (token input, add/delete, repo selector).
src/app.js	Wires feature flag + creates BYOT controls in the main app.
playwright/app.spec.ts	Adds tests for feature-flag visibility and persistence across reload.
docs/media/byot-model-perms.png	Adds screenshot asset for PAT model permissions.
docs/byot.md	Adds BYOT setup guide (fine-grained PAT permissions + enablement).
README.md	Links to the BYOT guide.

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