feat: add config.yaml support for timeouts, concurrency, persistence

[yimsk]

Summary

• Add ~/.config/claws/config.yaml support for customizable timeouts, concurrency limits, CloudWatch window, and startup profile/region persistence
• Unify hardcoded constants (awsInitTimeout, maxConcurrentProfileFetches) into configurable FileConfig with thread-safe accessors
• Add --persist/--no-persist CLI flags to override config file persistence setting

Changes

New Features

• Config file support (internal/config/file.go): YAML-based config with Duration type for human-readable timeouts
• Configurable timeouts: aws_init, multi_region_fetch, tag_search, metrics_load
• Concurrency limit: max_fetches (default: 50)
• CloudWatch window: cloudwatch.window (default: 15m)
• Persistence: Save region/profile selection on change when enabled
• Startup config: Auto-apply profile/regions on launch

Refactoring

• Extract lock helpers (withRLock, doWithLock) to internal/config/lock.go
• Remove duplicate constants from internal/app/app.go and internal/aws/init.go
• Atomic config save via temp file + rename pattern

Documentation

• README updated with config file example and CLI flags

Testing

• 284 lines of new tests in internal/config/file_test.go
• Duration marshal/unmarshal, save/load roundtrip, partial config, negative value handling
• All existing tests pass

Closes #67, closes #50

[claude]

Pull Request Review: Config File Support

Summary

This PR adds comprehensive configuration file support to claws, allowing users to customize timeouts, concurrency limits, CloudWatch windows, and persist profile/region selections. The implementation is well-structured with excellent test coverage (284 lines of new tests).

Code Quality & Best Practices ✅

Strengths:

1. Excellent separation of concerns: Config logic cleanly separated into file.go, lock.go, and comprehensive tests
2. Thread-safety: Proper use of sync.RWMutex with helper functions for safe concurrent access
3. Atomic writes: Config saving uses temp file + rename pattern (file.go:189-209) to prevent corruption
4. Custom YAML Duration type: Elegant solution for human-readable duration format
5. Graceful degradation: Missing config file returns defaults rather than errors

Minor Concerns:

1. Silent error handling in File() singleton (file.go:126-134)
If the config file exists but contains malformed YAML, the error is silently ignored. Users won't know their config is broken.
Recommendation: Log the error using the log package for diagnosability.

2. Error handling in persistence
In app.go:336-344 and app.go:366-376, config save errors are logged but don't notify the user. Consider showing a transient error message when persistence fails.

Performance Considerations ⚡

Config save I/O on every region/profile change
Every change triggers a synchronous file write (app.go:342, 373).

Impact: Minimal for most users, but could be noticeable on slow storage.
Recommendations: Consider debouncing saves or making them asynchronous. Current approach is acceptable for MVP.

Security ✅

• Config file permissions (0755) are acceptable since no secrets are stored
• Path traversal protection is correct (uses UserHomeDir + hardcoded path)
• YAML parsing is secure (gopkg.in/yaml.v3 with fixed types)

Consideration: Document that credentials should NEVER be added to this config (only in ~/.aws/credentials)

Test Coverage 📊

Excellent coverage with 284 lines covering:

• Duration marshal/unmarshal (including invalid values)
• Default config generation, missing file handling
• Save/load roundtrip, partial config with defaults
• Negative value handling, zero value getters

Nice-to-have additions: concurrent access tests, save failure scenarios, malformed YAML handling

Verdict

This is a high-quality PR that adds significant value. The code is well-structured, thread-safe, and thoroughly tested.

Required changes: None

Recommended improvements (post-merge):

1. Add error logging for malformed config files in File()
2. Consider user notification for persistence failures
3. Add concurrent access tests for extra confidence

Recommendation: APPROVE ✅

Great work! The atomic file writes, thread-safe design, and comprehensive test coverage demonstrate strong engineering practices.