Prepare version 0.3.1

[sudoHG]

Refs #182.

Summary

Set the shared product version to 0.3.1 and record the approval presentation and expiry fixes shipped by #181.
This PR is the version step of #182; tagging, signed build, device checks, notarization and publication follow its separate approval gates.

Diff stat

Two files changed, 9 insertions and 1 deletion: AskKeyVersion.swift and CHANGELOG.md.
Base: f99baf77cb03b0a5b13df7865bcea521ef0bf62a.
Head: 1f81acade2f634d2e6099aab86e76f9af76edfba.

Tests

• swift build -j 2: passed.
• swift test -j 2 --filter HelperMCPConnectionTests: 4 passed, 0 failed, 0 skipped.
• python3 -m unittest discover -s Tests/Automation -p test_product_version.py -v: 5 passed, 0 failed, 0 skipped.
• The selected test definitions are unchanged from main; no local baseline rerun, full suite or desktop UI flow was run. Full-suite and desktop acceptance come from this PR's CI.
• PR CI: both build-and-test and basic-ui-flows passed. Swift: 1,127 passed, 0 failed, 3 opt-in tests skipped; Automation: 183 tests passed; required desktop flows: 15 passed, 0 failed, 0 skipped.
• Base push CI has the same Swift counts and the same three opt-in skips: installed Codex CLI contract, abrupt file-commit subprocess, and synthetic native-bootstrap fixture generation.

Checks

• python3 scripts/check_hygiene.py: passed, zero violations.
• python3 scripts/check_module_deps.py: passed.
• git diff --check: passed.
• Data volume had 377 GiB free before building and 376 GiB before focused tests.

Deviations and questions

The maintainer waived the full independent pre-release review in #182. The signed release still requires the specified quick device check before notarization.
This PR references rather than closes #182 because the release must be published and verified before that task is complete.