release: publish stable v3.1.0

[ImYourBoyRoy]

What changed

• Promote the package to stable v3.1.0 with one stable-only release workflow.
• Add explicit first-run personalization questions to the canonical contract.
• Remove hard-coded client and integration software versions from README compatibility summaries.
• Adopt the pinned actions/setup-python v7 update and synchronize release inventory.
• Preserve the Antigravity two-fragment loader as a functional compatibility requirement.

Validation

• python3 scripts/validate_bundle.py
• python3 scripts/inspect_contract.py source
• python3 scripts/inspect_tree.py . --exclude .git --exclude .env
• python3 tests/run_portable_tests.py
• git diff --check

The stable archive and checksum will be built from the merged clean release commit.