fix: config inheritance precedence (project > global > default)

[bmdavis419]

Summary

• resolve effective model/provider/settings using project override -> global -> default
• add regression coverage for inheritance behavior

Issues

• Closes Global configuration is being overridden with built-in default #172

Greptile Summary

Fixes config inheritance by implementing proper field-level fallback (project > global > default). Previously, if a project config existed, all fields came from it even when undefined - now each field properly inherits from global config when not specified in project config.

• Replaced getActiveConfig() with individual getter functions for model, provider, providerTimeoutMs, and maxSteps
• Each field now uses proper nullish coalescing: currentProjectConfig?.field ?? currentGlobalConfig.field ?? DEFAULT
• Improved path handling by replacing string concatenation with path.join() and path.dirname() for cross-platform compatibility
• Added regression test verifying that project configs without provider/model inherit from global config

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• Clean implementation of the intended behavior with comprehensive test coverage. No breaking changes detected - the new behavior is more correct than the old. Path handling improvements are safe refactors. All existing tests should continue passing.
• No files require special attention

Important Files Changed

Filename	Overview
apps/server/src/config/index.ts	Implements proper config field inheritance (project > global > default) and improves path handling with path.join/dirname
apps/server/src/config/config.test.ts	Adds comprehensive test coverage for config inheritance when project config omits provider/model/settings

_{Last reviewed commit: 43bc6bc}