docs: add Mesh & P2P features section to README

- Full table of mesh networking modules
- FAPP protocol explanation with code example
- Privacy model summary
- Link to protocol spec

README.md

@@ -129,6 +129,61 @@ quicprochat/
 - **Dynamic plugins** — load `.so`/`.dylib` at runtime via `--plugin-dir` (6 hook points)
 - **Mesh networking** — iroh P2P, mDNS discovery, store-and-forward, broadcast channels
 
+### Mesh & P2P Features
+
+The `quicprochat-p2p` crate provides a full **serverless mesh networking stack**:
+
+| Feature | Module | Description |
+|---------|--------|-------------|
+| **P2P Transport** | `P2pNode` | Direct QUIC connections via iroh with NAT traversal |
+| **Mesh Identity** | `MeshIdentity` | Ed25519 keypairs with 16-byte truncated addresses |
+| **Mesh Envelope** | `MeshEnvelope` | Encrypted, signed, TTL-aware message containers |
+| **Store-and-Forward** | `MeshStore` | Queue messages for offline recipients |
+| **Multi-Hop Routing** | `MeshRouter` | Distributed routing table, forward through intermediaries |
+| **Announce Protocol** | `MeshAnnounce` | Signed peer discovery with capability flags |
+| **Broadcast Channels** | `BroadcastManager` | Pub/sub with symmetric key encryption |
+| **Transport Abstraction** | `TransportManager` | Iroh, TCP, LoRa — route by address type |
+| **LoRa Transport** | `transport_lora` | Duty-cycle aware, fragmentation, SF12 support |
+| **MLS-Lite** | `mls_lite` | Lightweight symmetric mode for constrained links |
+| **FAPP** | `fapp` + `fapp_router` | Free Appointment Propagation Protocol (see below) |
+
+#### FAPP — Decentralized Appointment Discovery
+
+**Problem:** In Germany, finding a psychotherapist takes 3–6 months due to artificial slot visibility limits.
+
+**Solution:** FAPP lets licensed therapists announce free slots into the mesh. Patients discover and reserve slots anonymously — no central registry.
+
+```rust
+// Therapist publishes slots
+let announce = SlotAnnounce::new(
+    &therapist_identity,
+    vec![Fachrichtung::Verhaltenstherapie],
+    vec![Modalitaet::Praxis, Modalitaet::Video],
+    vec![Kostentraeger::GKV],
+    "80331", // PLZ only, never exact address
+    slots,
+    approbation_hash,
+    sequence,
+);
+fapp_router.broadcast_announce(announce)?;
+
+// Patient queries anonymously
+let query = SlotQuery {
+    fachrichtung: Some(Fachrichtung::Verhaltenstherapie),
+    plz_prefix: Some("803".into()),
+    kostentraeger: Some(Kostentraeger::GKV),
+    ..Default::default()
+};
+fapp_router.send_query(query)?;
+```
+
+**Privacy model:**
+- Therapist identity is **public** (bound to Approbation hash)
+- Patient queries are **anonymous** (no identifying information)
+- Reservations use **E2E encryption** to therapist's key
+
+See [`docs/specs/fapp-protocol.md`](docs/specs/fapp-protocol.md) for the full protocol spec.
+
 ### Client SDKs
 
 | Language | Location | Transport | Notes |