feat(pi-fff): add compact clickable rendering for search tools

Summary

Add a compact TUI presentation for ffgrep and fffind in the Pi extension.

• Show a one-line tool header and one-line result preview by default.
• Click either part of a tool block to toggle the complete result.
• Keep ffgrep header options consistent: explicit limit and context render together as (limit N, context N).
• Do not change search execution, tool arguments, or model-visible tool results.

Verification

• tsc --noEmit
• bun test test/extension.test.ts