Add project documentation and linter config

CLAUDE.md

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+# repository rules
+
+* never use `git add -A` - add specific changes to a deliberate commit.  a
+  commit should contain one change.  after each change, make a commit with a
+  good one-line summary.
+
+* NEVER modify the linter config without asking first.
+
+* NEVER modify tests to exclude special cases or otherwise get them to pass
+  without asking first.  in almost all cases, the code should be changed,
+  NOT the tests.
+
+* when linting, assume the linter config is CORRECT, and that each item
+  output by the linter is something that legitimately needs fixing in the
+  code.
+