fix: select a compatible Python for smoke tests

[rogerchappel]

Summary

• add a deterministic Python >=3.11 resolver with an explicit STACKFORGE_PYTHON override
• use the resolved interpreter for generated Python API smoke validation
• add host-independent selection and rejection regressions and document the contributor prerequisite

Commits

• 167a22a test: verify Python interpreter resolution
• 8dea7d7 fix: resolve compatible Python for smoke tests
• 841f3d5 docs: document Python smoke prerequisite

Verification

• corepack pnpm install --frozen-lockfile
• corepack pnpm run release:check
• git diff --check origin/main...HEAD

The full release gate passed using /opt/homebrew/bin/python3.13; resolver regressions use isolated fake interpreters and do not depend on the host default.

[rogerchappel]

Automated merge note

Triage class: auto-merge

Summary: Deterministically resolves a supported Python >=3.11 interpreter for generated Python-project smoke tests, adds host-independent resolver regressions, and documents the contributor prerequisite (5 files, +82/-2).

Checks run: Node 20 compatibility, Node 22 compatibility, Repository hygiene, Docs hygiene, Generate branchbrief, and Release dry run — all COMPLETED/SUCCESS; originating worker ran corepack pnpm install --frozen-lockfile, corepack pnpm run release:check with Python 3.13, host-independent resolver regressions, and git diff --check. Final full diff, mergeability, branch protection, exact Roger Chappel author/committer identities, and head SHA re-verified.

Rebased/CI-repaired: No.

Verified head SHA: 841f3d5.