ux: surface a '+200…' indicator when untracked-file count hits the iteration cap #563

Problem

`compute_diff_stats` in `src-tauri/src/git_info.rs:277` enforces `MAX_UNTRACKED_FILES = 200` so a misconfigured repo (fresh `node_modules`, `dist/` not gitignored, large generated asset directory) can't pin a Tauri worker by making the badge sum thousands of files.

The cap is silent — the badge just reports the count for the first 200 untracked files. A user with 5,000 untracked files in a borked checkout sees "+12k" instead of "+300k" without any indication that the number is truncated.

Fix

Bubble a `untracked_truncated: bool` flag back from `compute_diff_stats` to `GitStatus`. Frontend (`src/pane.ts` footer render) appends a "…" or "+" suffix when truthy:

```
+12k+ (instead of +12k)
```

Matches htop / Activity Monitor convention for "more than this fits".

Why this matters

The cap exists for safety, but silently truncating UX signal is the kind of small lie that erodes trust in the rest of the badge over time. "This number is probably wrong" is more useful than a wrong number.

Files

• `src-tauri/src/git_info.rs:277-345` (compute_diff_stats — return truncated flag)
• `src-tauri/src/git_info.rs:80` (GitStatus struct — new field)
• `src/tab-state.ts` (GitStatusInfo interface)
• `src/pane.ts` (footer badge render)