chore: remove --use-pip flow and always use uv

[karakanb]

Summary

• Remove flag from run command and config path.
• Delete legacy local/venv python executor implementations and tests.
• Switch Python local execution to uv-only setup.
• Move shared command runner logic into .
• Update telemetry/docs and tests for uv-only flow.

Validation

• make format
• make test
• make integration-test-light

[greptile-apps]

Comments Outside Diff (1)

1. pkg/scheduler/scheduler.go, line 128-148 (link)

   Pre-existing JSON tag mismatch was cleaned up by this removal.

   The removed field UsePip had an incorrect JSON tag json:"useUV" — the opposite of what it should be. This would have caused any persisted RunConfig JSON using the key "usePip" to be silently ignored during deserialization, while the key "useUV" would incorrectly populate a field named UsePip. Removing it entirely is the correct resolution of this data integrity bug.

_{Last reviewed commit: 2ca37fc}