feat(tui): add Tab key to toggle JSON pretty-print

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>

Cargo.lock

@@ -2327,6 +2327,7 @@ dependencies = [
  "crossterm",
  "log-viewer-core",
  "ratatui",
+ "serde_json",
 ]
 
 [[package]]