Update CLAUDE.md with learnings

CLAUDE.md is the project's institutional knowledge — the things a new developer (or a new Claude session) needs to know that aren't obvious from the code itself. The goal is to keep it concise, current, and high-signal.

What belongs in CLAUDE.md

Include information that saves future sessions from re-discovering things the hard way:

• Conventions and philosophy — e.g., "Prefer composition over inheritance", "No backwards compatibility unless explicitly requested"
• Non-obvious gotchas — Things that cause repeated bugs or confusion
• Build/test/run commands — How to run, test, lint, deploy
• Project structure — Key directories and their purpose, especially if the layout is non-standard
• Recent significant changes — New capabilities, major refactors, or architectural shifts that change how the project works

What does NOT belong

Skip anything that's either ephemeral or derivable from the code: