Improve VS Code diff and graph comparison experience

[forhappy]

What changed

• add a VS Code-style top accent and raised active surface to the Ask Codebase tabs
• render Codebase Evolution source changes with @pierre/diffs, including split/unified modes, wrapping, responsive layout, file collapsing, and raw-patch fallback
• make versioned graph comparisons status-first with Added/Removed/Changed/Context filters, readable Git colors, quieter context nodes, bounded labels, and secondary community controls
• move source navigation selections through the beginning of the line after a node's recorded end line
• add browser coverage for the tab state, source diff renderer, and graph comparison controls

Why

The query tabs did not clearly communicate which mode was active, raw patches were difficult to scan, and graph deltas mixed change state with community and confidence styling. Source navigation also left the cursor on the recorded last line instead of immediately below the selected range.

User impact

Users can identify the active query mode at a glance, review revision diffs in a familiar code-review layout, isolate graph changes by status, and continue editing directly below a selected graph node's source range.

Validation

• TypeScript checks for all JavaScript workspaces
• 88 unit tests
• 57 Playwright browser and accessibility tests
• production VS Code extension build
• VSIX package and smoke check
• graphify update .