Make QDN relaying unconditional

[QuickMythril]

Summary

• remove the inherited relayModeEnabled operator switch and writable setting
• always relay QDN discovery, metadata, and chunks whenever QDN is enabled, subject to existing safety controls
• keep the legacy relay-status endpoint as deprecated and always true
• keep storagePolicy, blocking, capacity, hop/time, queue/backpressure, and qdnEnabled behavior separate
• accept legacy settings files containing relayModeEnabled without allowing the value to disable relay
• bound relay-cache persistence by configured QDN and filesystem headroom; use atomic staged writes and recover stale staging files

Validation

• complete local Maven suite: 2,630 tests, 0 failures, 0 errors, 64 skipped
• focused relay/storage/API suite: 55 tests passed
• real file-list relay regression covers legacy relayModeEnabled: false, multi-holder forwarding, hop/ID/hash preservation, and direct-request behavior
• relay-cache tests cover admission, overwrite accounting, atomic failure preservation, and crash-orphan recovery
• GitHub Maven, OSV, and all CodeQL checks passed
• git diff --check

Companion Node PR: QortiumDev/qortium-node#11

[QuickMythril]

Companion Node settings-UI cleanup: QortiumDev/qortium-node#11