When merging TOML configs, common config keys were appearing before
custom config keys. Add reorderMergedKeys() to ensure custom config
keys (model_provider, model, etc.) appear at the top, with common-only
keys appended after.
Add comprehensive config merge utilities for both Rust backend and TypeScript frontend
to support the new common config architecture where customConfig overrides commonConfig.
Backend (Rust):
- Add config_merge.rs module with JSON and TOML merge functions
- Support deep merge where source overrides target for nested objects
- Add extract_difference functions to identify custom-only keys
- Include compute_final_*_config functions for runtime merge calculation
- Register module in lib.rs
Frontend (TypeScript):
- Add configMerge.ts with isPlainObject, deepClone, deepEqual, deepMerge utilities
- Implement computeFinalConfig for merging common + custom configs
- Add extractDifference to identify keys unique to live config
- Add tomlConfigMerge.ts with TOML-specific merge/extract functions
- Use smol-toml for parsing and serialization
These utilities form the foundation for the refactored common config system
where providers store only custom config and merge with shared templates at runtime.