chore: finalize v0.1.0 release date

[nmogil]

Summary

Finalize the v0.1.0 changelog date after #21 merged and before creating the release tag.

Advances #20.

Change

• Replace the 0.1.0 changelog placeholder with the verified release date: 2026-07-15.

Post-merge release verification already completed

From merged main (4aadcd22c425d1ce5748031dc940b3f9c646417e):

• pytest -q -m 'not daytona_smoke' — 140 passed, 1 manually gated Daytona test deselected, 1 upstream Harbor deprecation warning
• explicit Docker smoke — 1 passed
• Ruff — passed
• strict mypy — passed across 17 source files
• wheel and sdist — built successfully
• truly clean wheel install with PYTHONPATH unset — passed
• credential-free sample — 2 records generated and validated
• current checkout and history credential-pattern scan — zero findings
• anonymous immutable runtime manifest fetch — passed
• immutable Daytona runtime contract inspection — passed for:
  ghcr.io/mogilventures/mogil-bench-daytona-runtime@sha256:7728671c38220e066d23f63fd2544cc0722874ec40e1c86c883c8cc4d6c35dfe

Repository activation completed

• corrected public repository description
• added release-relevant topics
• enabled active default-branch ruleset requiring PRs, blocking deletion and non-fast-forward updates, and requiring conversation resolution without mandatory approvals

After this PR merges

• verify merged main
• create annotated v0.1.0 tag
• create GitHub pre-release/public alpha with wheel and sdist assets
• verify tag/release/assets and close Prepare Mogil Bench v0.1.0 public-alpha release #20

PyPI remains deferred.