Agents page: collapse anatomy into icon cards → pretty editable modal

The agent command center's BRAIN+SURFACE columns are now a grid of compact icon
cards (system prompt / how it operates / personality / skills / capabilities /
tools / memory / safety). Clicking a card opens a modal with the full content,
nicely formatted (markdown/persona/tags), editable for the four brain text files
(system_prompt, agent_md, persona, skills_md) and saved back to the .brain via
PATCH /api/claws/{id}/brain. Capabilities/tools/memory/safety render read-only
(tools keeps its Add affordance). LIVE column unchanged.

- frontend: new AnatomyGrid (icon cards + SectionModal); ClawCommandCenter swaps the
  two verbose columns for it; skills_md added to RawBrain types.
- backend: cm-brain skills_md() getter + skills_md in ClawBrainResponse so the skills
  editor pre-fills (avoids blank-overwrite).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

frontend/src/components/dashboard/anatomy-cards.tsx

@@ -61,6 +61,7 @@ export type RawBrain = {
   system_prompt: string | null;
   agent_md: string | null;
   personality: string | null;
+  skills_md: string | null;
   skills: { name: string; body: string }[];
   tools: { name: string; state: string }[];
   memory: string[];