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/.fingerprint/signature-bdba74553465201a/lib-signature.json

@@ -0,0 +1 @@
+{"rustc":1100337564441796057,"features":"[\"alloc\", \"std\"]","declared_features":"[\"alloc\", \"derive\", \"digest\", \"rand_core\", \"std\"]","target":14677263450862682510,"profile":15657897354478470176,"path":8286560350723736022,"deps":[],"local":[{"CheckDepInfo":{"dep_info":"debug/.fingerprint/signature-bdba74553465201a/dep-lib-signature","checksum":false}}],"rustflags":[],"config":2069994364910194474,"compile_kind":0}