feat(fapp): add integration demo + update status

examples/fapp_demo.rs:
- Therapist publishes SlotAnnounce
- Relay caches and handles query
- Patient sends SlotQuery, gets response
- Shows full FappRouter API flow

docs/status.md:
- Updated FAPP integration status
- FappRouter now implemented
- Remaining: multi-node test, SlotReserve/Confirm, LoRa

crates/quicprochat-p2p/Cargo.toml

@@ -39,3 +39,7 @@ thiserror        = { workspace = true }
 
 [dev-dependencies]
 tempfile = "3"
+
+[[example]]
+name = "fapp_demo"
+path = "../../examples/fapp_demo.rs"