Move Common Commands to docs/COMMANDS.md and add docs/CONVENTIONS.md
for frontend patterns (SWR, filters, Mantine, routing, API URLs).
CLAUDE.md now only contains runtime rules and pointers.
Move architecture, testing, and dev tools detail into docs/ and
reference them via @path pointers to keep CLAUDE.md slim.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
