fix: remove chromadb <0.7 upper bound — blocks 1.x installs

The current constraint `chromadb>=0.5.0,<0.7` forces pip to install
chromadb 0.6.x, but palaces created with chromadb 1.x (which is what
the mempalace dev environment actually uses — 1.5.7 per uv.lock) have
an incompatible SQLite schema. Specifically, chromadb 0.6.x fails with
`KeyError: '_type'` when opening a collection written by 1.x.

This means a fresh `pip install mempalace` gives users a chromadb
version that cannot read palaces created in the maintainer's own
environment. The fix removes the upper bound so pip can resolve to the
current stable chromadb release.

Reproduction:
  python3 -m venv .venv && source .venv/bin/activate
  pip install mempalace          # installs chromadb 0.6.3
  # Try opening a palace created with chromadb 1.x:
  # -> _get_collection() returns None, tool_status() returns "No palace found"
  pip install chromadb==1.5.7    # force upgrade
  # -> tool_status() returns real data (26k drawers in our case)

pyproject.toml

@@ -25,7 +25,7 @@ classifiers = [
     "Topic :: Utilities",
 ]
 dependencies = [
-    "chromadb>=0.5.0,<0.7",
+    "chromadb>=0.5.0",
     "pyyaml>=6.0,<7",
 ]