feat(sync): apply selective replication scopes

[LimiNode]

Summary

• add bounded scope-local pull/push/apply to SyncEngine
• persist mutually exclusive full-global / selective receiver mode and exact duplicate evidence
• expose selective capability methods through ISyncPeer and DirectSyncPeer
• add foreground SelectiveSyncWorker paging with durable cursor resume
• document the implemented engine phase in the paired EN/RU design guides

Stack

This Draft PR is stacked on #330 (codex/selective-sync-protocol). It must be reviewed and merged after that protocol PR.

Contract

• scoped apply never advances _mdbxc_applied
• the first committed raw delivery mode is durable and mixing global/scoped streams fails closed
• multiple selective scopes are admitted only through disjoint immutable descriptors
• scoped pull is served only by the designated writer, so a receiver cannot become a relay
• scoped snapshots, persisted snapshot resume, retention/pruning, HTTP/WebSocket routing, and background scheduling remain out of scope

Validation

C++11 and C++17 MinGW CTest:

• test_sync_engine
• test_sync_stores
• test_sync_worker
• test_sync_replication
• test_sync_capture
• test_sync_randomized
• test_sync_randomized_lifecycle
• test_selective_replication_protocol
• header_sync_umbrella_test
• header_domain_mdbx_containers_sync_storage_hpp
• header_domain_mdbx_containers_sync_engine_hpp
• agent_policy_checks

Also built test_sync_stress in both language modes. git diff --cached --check passed before commit.