Add automatic canvas layout

[arjunkomath]

Summary

• add a desktop-only icon control that centers services in a spaced three-column canvas grid
• grow the canvas for larger or manually positioned layouts while preserving drag behavior
• persist manual and automatic position changes through one optimistic, rollback-safe SWR mutation
• add an authorized, validated, transactional batch position endpoint

Verification

• ./node_modules/.bin/tsc --noEmit
• npx biome check app/api/projects/[id]/services/route.ts app/api/projects/[id]/services/[serviceId]/position/route.ts components/service/service-canvas.tsx
• git diff --check
• Oracle review: approved with no remaining blockers

Test limitation

• Vitest could not start in the orb because Node 20.9 lacks APIs required by the installed pnpm/Vitest toolchain.

Basecamp task

[github-actions]

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_{Reviewed by React Doctor for commit bd6657c.}