[chore] add reusable standards layer

[salazarsebas]

Summary

This PR completes Phase 4 of the roadmap by introducing a reusable standards layer for common contract controls in Cougr.

It adds storage-backed, example-independent primitives for:

• Ownable
• Ownable2Step
• AccessControl
• Pausable
• ExecutionGuard
• RecoveryGuard
• BatchExecutor
• DelayedExecutionPolicy

Why

Cougr already had useful ECS, account, and privacy building blocks, but it did not yet expose a cohesive standards layer for common contract ergonomics and operational controls.

This change closes that gap with explicit, composable primitives that:

• avoid game-specific assumptions
• keep storage schemas deterministic through namespaced Symbol identifiers
• define clear error semantics and typed transition events
• integrate cleanly with the existing crate structure instead of introducing a parallel architecture

Impact

Developers building on Cougr now have a dedicated public standards surface for ownership, access control, pausability, guarded execution, recovery-aware protection, bounded batching, and delayed execution flows.

The documentation and maturity model were also updated so the new layer is described honestly as Beta and aligned with the roadmap and public API story.

Validation

• cargo fmt --check
• cargo test --test integration_standards -- --nocapture
• cargo test --test public_api_surface -- --nocapture
• cargo test --lib --tests

Closes #101