feat: add a user configuration to enable arrow keys to move the cursor

[bilboquet]

Description

This PR adds the support for arrow keys in navigation mode. I need this because I use the "bepo" layout, so h,j,k and l are dispersed around my keyboard, and it does not make much sense to use them for navigating.
Remapping c,t,s and r - that are at the same place as h,j,k and l - would conflict very badly helix key bindings.
I hope this would be useful to other non "standard" keyboard layout.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Related Issues

Closes #

Changes Made

• add app_config module

Testing

Test Results

• All existing tests pass (cargo nextest run --lib)
• Added new tests for new functionality
• Manual testing completed

# Test commands run
cargo nextest run --lib
cargo clippy -- -D warnings
cargo +nightly fmt -- --check
cargo deny check

Test Coverage

• I test that arrow keys behave like h,j,k and l

Screenshots/Demo

Checklist

• Code follows the project's style guidelines
• Self-review of code completed
• Comments added for complex logic
• Documentation updated (if applicable)
• No new warnings generated
• Tests added/updated and passing
• CLAUDE.md updated (if architecture changed)
• README.md updated (if user-facing changes)

Performance Impact

• No performance impact
• Performance improved
• Performance impact assessed and acceptable

Security Considerations

• No security impact
• Security review completed
• Input validation added/updated

Additional Notes

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.22222% with 28 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/main.rs	0.00%	16 Missing ⚠️
src/input/handlers.rs	95.53%	8 Missing ⚠️
src/ui/state/substates.rs	57.14%	3 Missing ⚠️
src/config/app_config.rs	99.30%	1 Missing ⚠️

@@            Coverage Diff             @@
##             main     #153      +/-   ##
==========================================
+ Coverage   91.58%   91.59%   +0.01%     
==========================================
  Files         123      124       +1     
  Lines       24921    25279     +358     
==========================================
+ Hits        22823    23154     +331     
- Misses       2098     2125      +27     

Flag	Coverage Δ
unittests	91.59% <92.22%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/ui/state/mod.rs	67.66% <100.00%> (+1.16%)	⬆️
src/config/app_config.rs	99.30% <99.30%> (ø)
src/ui/state/substates.rs	96.75% <57.14%> (-1.56%)	⬇️
src/input/handlers.rs	90.77% <95.53%> (+1.23%)	⬆️
src/main.rs	0.00% <0.00%> (ø)

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[Copilot]

Pull request overview

This PR adds a user-configurable option to enable arrow keys for cursor movement in normal mode, specifically designed to help users with non-standard keyboard layouts (like bépo) where h/j/k/l keys are not conveniently positioned for navigation.

Changes:

• Added persistent application configuration storage system with JSON serialization
• Introduced enable_arrow_keys_in_normal_mode configuration option that maps arrow keys to h/j/k/l movement commands in normal mode
• Modified application state initialization to support custom configuration via new with_config method

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/config/app_config.rs	New module implementing configuration storage and persistence with JSON serialization to ~/.config/helix-trainer/config.json
src/config/mod.rs	Added app_config module and exports for AppConfig and ConfigStorage
src/ui/state/substates.rs	Added enable_arrow_keys_in_normal_mode boolean field to ConfigState with default value of false
src/ui/state/mod.rs	Added with_config method to support custom configuration initialization while maintaining backward compatibility with existing new method
src/main.rs	Integrated configuration loading on startup and saving on exit, with error handling and logging
src/input/handlers.rs	Implemented arrow key to h/j/k/l mapping logic with conditional behavior based on configuration, including comprehensive tests

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[bug-ops]

PR Review

Thanks for the contribution! Arrow key support for non-standard keyboard layouts like bépo is a useful feature.

I've reviewed the implementation and found a few issues that should be addressed before merging.

Summary

✅ Good:

• Clean implementation following existing ProfileStorage pattern
• Feature is opt-in (disabled by default)
• Good test coverage

⚠️ Issues to address:

1. Error handling uses Result<_, String> instead of proper error types
2. Field duplication between AppConfig and ConfigState
3. Config is saved on every exit regardless of changes

See inline comments for specific suggestions.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

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[bug-ops]

Hey, @bilboquet! Great implementation! A few items to consider for future PRs:

1. ConfigData wrapper simplification - The ConfigData struct wraps AppConfig to produce {"config": {...}}
   JSON. Consider serializing AppConfig directly to reduce indirection.

2. Config load error visibility - When malformed config exists, we silently fall back to defaults. Users might not
   realize their config was ignored. Consider adding a user-visible warning on next startup.

3. ConfigState::reset() behavior - Currently resets all fields including persistent config (arrow keys setting).
   Clarify: should persistent settings survive filter resets, or is the current behavior intentional?

These don't block the PR but worth revisiting when refactoring config handling.