Add File Explorer screen for selecting Bitcoin config file

[R27-pixel]

Changes:

• Add FileExplorer component to handle directory reading and navigation
• Introduce FileExplorer screen state
• Render file list when FileExplorer screen is active
• Allow navigation from "Bitcoin Config" into File Explorer via Enter
• Save selected file path to app.bitcoin_conf_path

Interaction flow:

1. Navigate to "Bitcoin Config"
2. Press Enter to open File Explorer
3. Navigate files
4. Press Enter to select a file

[codecov]

Codecov Report

❌ Patch coverage is 94.70199% with 16 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/main.rs	89.18%	12 Missing ⚠️
src/components/file_explorer.rs	98.06%	3 Missing ⚠️
src/ui.rs	97.05%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[pool2win]

Generally looks good, but we are missing unit tests and comments on structs and functions.

[pool2win]

Looking much better now. Writing comments and unit tests is even more important in the LLM era, these help LLMs write better code and detect errors.

Next thing. If you look at the codecov report you can see we are missing coverage on 17 lines, if you dig into the report https://app.codecov.io/gh/p2poolv2/pdm/pull/8?src=pr&el=tree you can see that it is because we haven't written tests for a) wrapping around the index and b) setting selected field. Please add tests to cover those cases too.

[R27-pixel]

Looking much better now. Writing comments and unit tests is even more important in the LLM era, these help LLMs write better code and detect errors.

Next thing. If you look at the codecov report you can see we are missing coverage on 17 lines, if you dig into the report https://app.codecov.io/gh/p2poolv2/pdm/pull/8?src=pr&el=tree you can see that it is because we haven't written tests for a) wrapping around the index and b) setting selected field. Please add tests to cover those cases too.

Added
integration coverage for file explorer selection and wrap

[pool2win]

The codecov report still is below 90% for the file_explorer module. The parts about going to parent directory are untested. https://app.codecov.io/gh/p2poolv2/pdm/pull/8?src=pr&el=tree#fb36e13b4d2998c3c08398594680d935-R105 Let's add tests for those.

[pool2win]

Sweet. Thanks.