Add AppMode enum (Normal/Settings), level_cache field populated in recompute_wrap_cache via detect_level(), color_config loaded from TOML in main.rs. Refactor handle_key for mode dispatch with S key to enter settings.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
Press Tab to switch JSON log lines between raw single-line and indented
multi-line format (2-space indent, like jq output). Only JSON Object lines
are affected; plain text lines stay unchanged.
- Add json_format bool field to App, toggled by Tab
- Add format_json_line() standalone function with serde_json::to_string_pretty
- Integrate into recompute_wrap_cache with \n-split sub-line wrapping
- Center viewport on cursor after cache rebuild to prevent jump on toggle
- Add 12 unit tests covering format, toggle, and edge cases
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
