feat(fapp): add FappRouter for mesh integration

New fapp_router.rs module:
- FappAction enum (Ignore, Dropped, Forward, QueryResponse)
- Wire format: 1-byte tag (0x01-0x05) + CBOR body
- FappRouter with shared RoutingTable and TransportManager
- handle_incoming() decodes and dispatches FAPP frames
- process_slot_announce() with relay/flood logic
- process_slot_query() answers from local FappStore
- broadcast_announce() / send_query() for outbound floods
- drain_pending_sends() for async send integration
- 3 unit tests

Also fixed borrow checker issue in FappStore::store

crates/quicprochat-p2p/src/fapp.rs

@@ -426,14 +426,14 @@ impl FappStore {
             }
         }
 
-        // Capacity check per therapist.
-        let queue = self
-            .announces
-            .entry(announce.therapist_address)
-            .or_default();
-        if queue.len() >= MAX_PER_THERAPIST {
-            // Evict oldest.
-            queue.remove(0);
+        let addr = announce.therapist_address;
+
+        // Capacity check per therapist (evict oldest if needed).
+        {
+            let queue = self.announces.entry(addr).or_default();
+            if queue.len() >= MAX_PER_THERAPIST {
+                queue.remove(0);
+            }
         }
 
         // Total capacity check.
@@ -452,10 +452,9 @@ impl FappStore {
         }
 
         // Update latest sequence.
-        self.latest_sequence
-            .insert(announce.therapist_address, announce.sequence);
+        self.latest_sequence.insert(addr, announce.sequence);
 
-        queue.push(announce);
+        self.announces.entry(addr).or_default().push(announce);
         true
     }