fix(theme): restore GitHub Dark Default as the default theme

[benvinegar]

Summary

Restore github-dark-default as Hunk's default theme, verified against the parent of 6c95708 (#1128), which switched the default to terminal.

• Restore the configured GitHub Dark Default theme and GitHub light/dark fallback behavior.
• Keep terminal opt-in, including its live palette updates; keep explicit auto selection unchanged.
• Update default-theme expectations, add a real-PTY regression for a light terminal, and update documentation and the Changeset.
• Sync the packaged README and stabilize two PTY tests: use fixed wheel steps for an exact scroll roundtrip and wait for committed viewport/layout paint instead of transient frames.
• Reuse the existing async test-directory cleanup helper to handle transient Windows executable file locks.

This belongs in core because it changes the built-in launch default, not an optional workflow. No themes are removed.

Validation

All CI checks pass at 6013ad5, including Linux validation/packaging, PTY integration, Windows compatibility, macOS/Windows compiled portability, website, and Nix packaging. Local checks ran on Linux; macOS and Windows were not tested locally.

• Passed: bun run typecheck
• Passed: bun run test (both shards)
• Passed: bun run test:integration (265 passed, 1 platform skip)
• Passed: bun run test:tty-smoke (11 real-TTY tests)
• Passed: bun run check:pack
• Passed: bun run generate:docs
• Passed: formatting checks and commit-hook linting
• Passed: bun test test/pty/comment-target.test.ts test/pty/open-scroll-integration.test.ts five consecutive times

No before/after media is attached; visual verification is limited to the real-TTY/PTY tests.

This PR description was generated by Pi using GPT-6.1-sol

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1 Skipped Deployment

Project	Deployment	Actions	Updated
hunk-web	Ignored	Preview	Oct 16, 2026 6:26pm UTC

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge.

Summary

Restores github-dark-default as the launch default and GitHub light/dark themes as the fallback for missing theme ids.

• Hunk starts reviews with GitHub Dark Default unless you choose another theme.
• Choosing terminal still makes review colors follow terminal palettes.

_{Reviews (1) · Last reviewed commit: "fix(theme): restore GitHub Dark Default ..." · Reviewed by Greptile}