release: finalize v3.2.0 — version consistency + CHANGELOG

PR #761 bumped pyproject.toml to 3.2.0 but missed three other version strings,
causing test_version_consistency to fail on develop CI (macos, linux 3.11, windows).

- mempalace/version.py: 3.1.0 → 3.2.0 (unblocks test_version_consistency)
- README.md: version badge shield 3.1.0 → 3.2.0
- integrations/openclaw/SKILL.md: 3.1.0 → 3.2.0
- CHANGELOG.md: rename [Unreleased] → [3.2.0] — 2026-04-13, add entries
  for #685, #690, #707, #716, #734, #755, #757, #761

Verified locally: 689/689 tests pass, ruff clean.

integrations/openclaw/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: mempalace
 description: "MemPalace — Local AI memory with 96.6% recall. Semantic search, temporal knowledge graph, palace architecture (wings/rooms/drawers). Free, no cloud, no API keys."
-version: 3.1.0
+version: 3.2.0
 homepage: https://github.com/MemPalace/mempalace
 user-invocable: true
 metadata: