feat: initial meshservice implementation

Generic decentralized service layer for mesh networks.
Includes FAPP (psychotherapy) and Housing as reference services.

- ServiceMessage with Ed25519 signatures
- Wire protocol (64-byte header + CBOR)
- ServiceRouter with pluggable handlers
- Verification framework (3 trust levels)
- 32 tests, 3 examples

target/debug/build/serde-6bf5280d9408b79b/out/private.rs

@@ -0,0 +1,6 @@
+#[doc(hidden)]
+pub mod __private228 {
+    #[doc(hidden)]
+    pub use crate::private::*;
+}
+use serde_core::__private228 as serde_core_private;