refactor(store): Prepare store boundary for extraction

[leumor]

Summary

• prepare the network.crypta.store boundary for later extraction into a leaf module without creating :foundation-store yet
• move store stats contracts into :foundation-store-contracts and add a minimal store-maintenance alert SPI there
• move the support helper subset into :foundation-support, update ownership metadata, and add the required support dependencies
• replace direct store dependencies on runtime alert/UI classes with StoreAlertSink plus the new UserAlertManagerStoreAlertSink adapter
• narrow SlashdotStore to BucketFactory, switch SaltedHashFreenetStore to AtomicFileMoves.moveTo(...), remove MasterKeys usage from CipherManager, and add focused test coverage for the new boundary

How to test

./gradlew :foundation-support:compileJava :foundation-store-contracts:compileJava :compileJava
./gradlew test \
  --tests 'network.crypta.support.ByteArrayWrapperTest' \
  --tests 'network.crypta.support.LRUMapTest' \
  --tests 'network.crypta.support.io.NativeThreadTest' \
  --tests 'network.crypta.support.io.FallocateTest' \
  --tests 'network.crypta.support.WrapperKeepaliveTest' \
  --tests 'network.crypta.node.SemiOrderedShutdownHookTest' \
  --tests 'network.crypta.store.NullFreenetStoreTest' \
  --tests 'network.crypta.store.RAMFreenetStoreTest' \
  --tests 'network.crypta.store.SlashdotStoreTest' \
  --tests 'network.crypta.store.saltedhash.SaltedHashFreenetStoreTest' \
  --tests 'network.crypta.store.caching.CachingFreenetStoreTest'
./gradlew test --tests 'network.crypta.store.*' --tests 'network.crypta.store.saltedhash.*'
./gradlew test

[sonarqubecloud]

Quality Gate failed

Failed conditions
78.5% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud