fix(chat): sanitize preset command values

[tracerat]

Summary

• Give preset command-menu items a stable, selector-safe value.
• Normalize both preset titles and descriptions while keeping their displayed text unchanged.
• Add a regression test covering selector metacharacters in both fields.

Verification

• pnpm --dir frontend test agent-presets-builder
• pnpm --dir frontend run typecheck
• pnpm --dir frontend exec biome check src/lib/agent-presets.ts src/components/chat/chat-session-pane.tsx tests/agent-presets-builder.test.tsx

LOC

Category	+	-
Logic	19	1
Tests	22	0

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Summary by cubic

Sanitize chat preset command values so they’re selector-safe while remaining searchable. Keeps visible preset names/descriptions unchanged and prevents command-menu selector errors.

• Bug Fixes
  • Generate selector-safe, searchable values via buildAgentPresetCommandItemValue from preset titles/descriptions.
  • Add regression test covering quotes, brackets, and other selector metacharacters.

^{Written for commit fd8f360. Summary will update on new commits.}