feat(runtime): implement pilot runtime scroll replay

[drown0315]

Summary

Adds PilotRuntime-backed scroll replay and makes pilot_runtime the default Runtime Adapter path. The branch also fixes VM service numeric parameter parsing so scroll deltas sent through service extensions execute correctly.

What Changed

• Defaulted Flutter Pilot runtime selection to pilot_runtime and removed the old mcp_flutter adapter path.
• Added app-side scroll replay, text action support, and runtime protocol/client coverage in packages/pilot_runtime.
• Added smoke app scroll scenarios and docs for validating targeted scroll replay and non-scrollable failures.
• Added regression coverage for VM service numeric scroll parameters arriving as strings.

Why

Scroll replay needs to cross the real VM service extension boundary, where service extension parameters are delivered as strings. Parsing numeric extension parameters in the app-side runtime keeps Scenario scroll deltas compatible with real debug Runtime Targets.

Verification

• dart format .
• dart analyze
• dart test
• flutter test in packages/pilot_runtime

Notes

A local, unstaged edit remains in examples/smoke_app/pilot/pilot_runtime_scroll.yaml and is not part of this PR.