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

[RunMintOn]

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

[gustav-fff]

[triage-bot] LINKED PR: #852 (#852) — state: OPEN.

Single PR linked, Fixes #851. Touches only packages/pi-fff/src/index.ts (+102/-14) and packages/pi-fff/test/extension.test.ts (+83/-0).

What it does: adds a CollapsedText component that renders ffgrep/fffind call headers and results as one line (with ... (N more lines) suffix), wraps both in MouseRegion so a left click flips context.state.fffCompactExpanded and toggles the complete output. ffgrep header now joins explicit limit/context into a single (limit N, context N) group. The old renderTextResult is renamed renderPreviewResult and kept for the multi-grep tool, so tool schemas, execution paths and model-visible results are untouched.

No repro or fix work done from this side. Nothing further from triage; review is on the maintainer.

Honk-Honk 🪿