fix(tui): show completed write output

[kitlangton]

What

Show the syntax-highlighted file contents after the V2 write tool completes.

Before / After

Before: The write renderer used metadata.diagnostics as its completion signal. V2 writes do not emit diagnostics yet, so successful writes remained as a compact Write <path> row and hid the content already present in input.content.

After: A completed write switches to the existing code-block presentation based on the durable tool status. Diagnostics remain optional and render when available.

How

• packages/tui/src/routes/session/index.tsx keys the write block on state.status === "completed" instead of optional diagnostics metadata.
• Audited the other mutation renderers: edit and patch already key their expanded views from final diff/file metadata emitted by their V2 tools.

Scope

This does not add V2 LSP diagnostics to write or edit tools.

Testing

• bun typecheck in packages/tui
• bun run test test/mini/tool.test.ts test/mini/entry.body.test.ts test/mini/scrollback.surface.test.ts test/cli/tui/inline-tool-wrap-snapshot.test.tsx in packages/tui (49 passed)
• Repository pre-push typecheck (32 packages passed)

Demo

An OpenCode Drive before/after capture was attempted against origin/v2-migration. Drive 1.4.2 currently intercepts the unsupported write mutation and records session.tool.failed rather than a completed built-in write; its generated client also does not match this branch's session API. No misleading failed-tool recording is attached.