[codex] Refine agent visual style distinction

[rogerchappel]

Summary

• Give each Agent Mode visual a distinct style shell and secondary palette instead of tinting every element with the accent color.
• Make Hologram Waveform use a rounded rectangular/glass ribbon stage, Neural use secondary graph colors, and Command Core use operational grid/tick tones.
• Keep the custom accent for active highlights while fixed secondary/shadow colors carry style identity.
• Raise the Style modal above immersive Agent Mode and stop the color picker from committing every drag event.

Why

Testing showed the four styles still felt too similar, the custom color was washing every element, reactivity looked weak, the native color picker felt slow, and the Style modal opened behind immersive mode.

Verification

• pnpm typecheck
• pnpm test src/lib/agent-visual-settings.test.ts 'src/app/api/companies/[id]/route.test.ts'
• pnpm lint:check (existing warnings only)
• git diff --check origin/main...HEAD
• agent visual distinction smoke check
• push hook: pnpm typecheck and pnpm build