fix(compile): default non-1es pool vmImage to ubuntu-22.04

[Copilot]

Summary

Non-1ES pipelines were implicitly defaulting to pool.vmImage: ubuntu-latest; this updates the default to ubuntu-22.04 to make generated pool configuration explicit and stable. The change aligns compiler defaults, tests, and user-facing docs/prompts.

• Compiler default
  • Changed non-1ES default VM image constant from ubuntu-latest to ubuntu-22.04 in pool resolution logic.
• Type-level default + tests
  • Updated PoolConfig::default() and unit tests that assert default/non-specified VM image behavior.
• Codemod/docs consistency
  • Updated codemod comments/tests and front-matter/docs/prompt references that describe the non-1ES default value.

# Before (implicit non-1ES default)
pool:
  vmImage: ubuntu-latest

# After
pool:
  vmImage: ubuntu-22.04

Test plan

Validated via existing Rust test/build/lint pipelines for this repo.