chore(release): bump version strings to 3.3.0 and curate CHANGELOG

Prepare develop for the 3.3.0 release cycle.

Version bumps:
- mempalace/version.py: 3.2.0 -> 3.3.0
- pyproject.toml: 3.2.0 -> 3.3.0
- README.md: pyproject.toml label and shields.io badge
- uv.lock: mempalace 3.0.0 -> 3.3.0 (also fills in resolved dev/extras)

CHANGELOG.md:
- Close out the stale [Unreleased] section as [3.2.0] - 2026-04-12
  (v3.2.0 was tagged on that date but the release flip was never made)
- Add a fresh [Unreleased] - v3.3.0 section covering the 49 commits
  since v3.2.0: closet layer, BM25 hybrid search, entity metadata,
  diary ingest, cross-wing tunnels, drawer-grep, offline fact checker,
  LLM-based closet regen, hall detection, cosine-distance fix,
  multi-agent locking, README audit, etc.
- Adopt Keep a Changelog + SemVer framing
- Add version compare reference links at the bottom
- Fix stale milla-jovovich/mempalace preamble URL to MemPalace/mempalace

README.md

@@ -714,7 +714,7 @@ mempalace/
 │   └── mcp_setup.md
 ├── tests/                     ← test suite (README)
 ├── assets/                    ← logo + brand assets
-└── pyproject.toml             ← package config (v3.2.0)
+└── pyproject.toml             ← package config (v3.3.0)
 ```
 
 ---
@@ -742,7 +742,7 @@ PRs welcome. See [CONTRIBUTING.md](CONTRIBUTING.md) for setup and guidelines.
 MIT — see [LICENSE](LICENSE).
 
 <!-- Link Definitions -->
-[version-shield]: https://img.shields.io/badge/version-3.2.0-4dc9f6?style=flat-square&labelColor=0a0e14
+[version-shield]: https://img.shields.io/badge/version-3.3.0-4dc9f6?style=flat-square&labelColor=0a0e14
 [release-link]: https://github.com/milla-jovovich/mempalace/releases
 [python-shield]: https://img.shields.io/badge/python-3.9+-7dd8f8?style=flat-square&labelColor=0a0e14&logo=python&logoColor=7dd8f8
 [python-link]: https://www.python.org/