Add CI, config, store, and test files

[pppmppp]

Summary

• Adds .gitignore, config.js, store.js, notes.js, notes.test.js, and ci.yml
• Sets up CI workflow and test infrastructure

Test plan

• CI workflow runs on push
• notes.test.js passes

🤖 Generated with Claude Code

[pppmppp]

Yes — Claude caught the bug: store.edit() crashes with TypeError: Cannot set properties of undefined when the given ID doesn't exist, because find() returns undefined and there's no null-check before note.text = text.