Polish repository viewer controls and lazy navigation #114

Make the small TypeScript repository viewer clearer to use while keeping the existing separate Spin API and minimal build.

Requested changes:

• Investigate and correct the branch dropdown's appearance in the Codex in-app browser.
• Rename Clone to Code, with a downward arrow on the right and an optional small code symbol on the left.
• Make commit entries links so users can explore history lazily, if this fits the existing API with little code.
• Use simple folder/file icons instead of arrows and bullets.
• Add a .. parent-directory entry inside folders.
• Show a truncated commit subject alongside displayed commit hashes where that information is available.

Keep reads lazy and sparse, preserve authorization and bounded reads, and avoid per-file history scans or new Go routes. Reuse the existing Preact/Bun/Biome setup and a small icon treatment rather than adding a UI dependency. Use the pushed object-log history to check real nested paths and commits; preserve the user's running demo and data.

Validation should include viewer lint, types, meaningful navigation tests, component build, and actual in-app browser checks. If an item needs substantial machinery, report the smallest alternative before adding it.