[codex] prepared approval actions

[nahiyankhan]

Summary

Adds prepared approval actions so approval-gated capabilities approve a host-prepared frozen request instead of raw generated args.

• Adds ApprovalPrepared and ApprovalRequest public types, optional approval.prepare(args), request ids in approval state, and ctx.approval for approved handlers.
• Keeps existing one-argument approval.request(args) callbacks source-compatible.
• Replaces demo window.confirm approval with small host-owned approval cards outside the sandbox.
• Updates adoption/security docs with the invariant that hosts prepare, users approve, and handlers execute the frozen plan.
• Adds unit and gallery e2e coverage for invalid args, prepared plans, request ids, approval, and denial.

Validation

• pnpm typecheck
• pnpm test
• pnpm test:gallery