Deliver opt-in Linux X11 Bluetooth runtime using read-v1 replies #726

Integrate BlueZ GATT read-v1 peer-scoped transport, existing authenticated protocol engine, persistent pairing-before-publication, bounded credential worker and X11 basic keyboard/text/pointer input. Single runtime owner with bounded ingress, peer/generation invalidation, disconnect/idle cleanup and honest reduced capabilities. Explicit development opt-in, no production release activation. Build on #725; target linux-support. Fake-only tests and independent latest-head review required before a supervised Android test.