fix(windows): improve Git diff viewing and history pagination

[yangboxuan726]

Summary

• paginate Windows Git history with cumulative snapshots and the shared Core hasMore state
• default the Windows diff viewer to a persistent IDEA-style split layout
• preserve Core-aligned old/new rows so unchanged replacements stay neutral and semantic line counts stay accurate
• resolve repositories from file paths before requesting diffs
• route Source Control files and diffs to the main editor pane even when the terminal pane is active

Root cause

The Windows client passed pathspecs and pagination parameters that did not match the shared Core contract. Split diffs were then reconstructed from independent vertical lines, which made unchanged paired lines appear as one deletion plus one addition. Source Control buffers could also be created in the active bottom pane, leaving them invisible while the Terminal tab was selected.

User impact

Windows users can page through Git history reliably, click changed files to open them in the editor, and review additions and deletions in an IDEA-style side-by-side view with accurate semantic counters.

Validation

• bun test — 28 tests passed
• bun run typecheck
• targeted vp lint
• git diff --check
• native Windows cold-start verification for opening and switching staged file diffs

Screenshots

Addition

Deletion