[Agent] Command palette lacks focus trap

Agent brief

Category: a11y | Severity: medium | Effort: S

Problem

Command palette dialog lacks focus trap. Tab key escapes to page behind modal.

Files

• src/components/search/command-palette.tsx
• Use Radix Dialog focus trap or @radix-ui/react-focus-scope

Acceptance criteria

• Focus trapped while palette open
• Escape closes and restores focus
• First result or input receives focus on open