chore: add push/PR CI, drop unused windows dep, refresh docs

Add a CI workflow running fmt, clippy with warnings denied, and the test
suite on every push and pull request. Remove the unused workspace windows
dependency now that only windows-sys is used. Update the README architecture
name and Java harness reference, clarify the plans gitignore comment, and
carry the code-reviewer agent memory.

.gitignore

@@ -21,5 +21,5 @@ Thumbs.db
 # Logs
 *.log
 
-# Plans (we keep the C# project's plans separate)
+# Plans (stateful working notes, not shipped docs)
 /plans/