docs(claude): prune CLAUDE.md to follow Anthropic best practices

Cut self-evident rules and content duplicated by skills/rules files
(architecture overview, naming conventions, integration walkthrough,
component/hook templates). Kept counter-intuitive Sim-specific rules
where Claude's defaults disagree with the codebase: withRouteHandler,
@sim/utils/id, React Query patterns, and vitest performance gotchas.

422 lines -> 117 lines.

Author: emir-karabeg