chore: tighten chromadb version range and add py.typed marker

- Tighten chromadb dependency from >=0.4.0,<1 to >=0.5.0,<0.7
  (the collection API changed significantly across majors; this
  pins to the tested range)
- Add optional 'spellcheck' extras for the undeclared autocorrect
  dependency used in spellcheck.py
- Add PEP 561 py.typed marker for type checker support

Findings: #10 (HIGH — chromadb range too wide), #30 (LOW — undeclared
          autocorrect), #32 (LOW — missing py.typed)

Includes test infrastructure from PR #131.
92 tests pass.

pyproject.toml

@@ -25,7 +25,7 @@ classifiers = [
     "Topic :: Utilities",
 ]
 dependencies = [
-    "chromadb>=0.4.0,<1",
+    "chromadb>=0.5.0,<0.7",
     "pyyaml>=6.0",
 ]
 
@@ -39,6 +39,7 @@ mempalace = "mempalace:main"
 
 [project.optional-dependencies]
 dev = ["pytest>=7.0", "ruff>=0.4.0"]
+spellcheck = ["autocorrect>=2.0"]
 
 [dependency-groups]
 dev = ["pytest>=7.0", "ruff>=0.4.0"]