Add CLAUDE.md and NOTES.md project docs

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: peterkudlicka

CLAUDE.md

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+# CLAUDE.md
+
+## Architecture
+- routes/users.js — the users resource, one route per action
+- db/store.js — the in-memory data helper all routes go through
+- tests/update-user.test.js — the tests
+
+
+

NOTES.md

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+# NOTES.md
+
+## Plan
+Plan the new endpoint "update a user" to 
+
+- update an existing user by id (PUT /users/:id)
+- validate the input, rejecting missing or invalid fields with a clear error
+- return a sensible "not found" response when the user doesn't exist, rather than crashing
+- go through db/store.js for data access, following the existing pattern
+
+The repo already contains the tests for this endpoint, in tests/update-user.test.js. They start red — making them pass is how 
+
+
+## Tasks
+
+[ ] Add the updateUser function to db/store.js
+[ ] Add the PUT /users/:id route to routes/users.js
+[ ] Add input validation (return 400 for missing fields)
+[ ] Add 404 handling for non-existent users
+
+## Commits
+First commit contains changes to db/store.js
+Second commit contains the creation of the new endpoint (+ input validation, 400 and 404 return responses)
+
+## Model
+I will use opusplan