fix(theme): match Herdr default palette

[RaviTharuma]

Summary

• use Catppuccin as the inherited fallback when Herdr has no explicit [theme].name
• keep One Light as Navigator's standalone palette when inherit_herdr = false
• cover missing and unknown theme names with regression tests

Fixes #5.

Checks

• cargo fmt --check — unavailable locally because the stable toolchain does not include rustfmt
• cargo clippy -- -D warnings — blocked by pre-existing clippy::items_after_test_module in src/main.rs
• cargo test — 67 passed, 2 pre-existing app tests failed (close_target_matches_entry_kind, source_specific_reuse_distinguishes_same_path_workspaces)
• cargo test theme::tests:: — 5 passed
• git diff --check

🤖 Generated with Claude Code

[RaviTharuma]

This is the preferred theme-fallback PR for #5. #10 was closed as a duplicate of this one.

[thanhdat77]

Thanks for identifying the Herdr fallback mismatch and providing the regression coverage. The equivalent fix has since landed on main in 2c83c80: inherited themes now fall back to Catppuccin for missing, unreadable, invalid, or unknown configuration, while inherit_herdr = false keeps One Light. Issue #5 is closed and the current suite passes.

Closing this PR as superseded to avoid merging duplicate changes. Thank you for the contribution.