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/ciborium-ll-88ab61518aa1cb64/lib-ciborium_ll.json

@@ -0,0 +1 @@
+{"rustc":1100337564441796057,"features":"[]","declared_features":"[\"alloc\", \"std\"]","target":6259365080488940533,"profile":15657897354478470176,"path":1511942723809443561,"deps":[[10057415176380654875,"ciborium_io",false,6186247551662299042],[16598877151661132269,"half",false,5047299574991150906]],"local":[{"CheckDepInfo":{"dep_info":"debug/.fingerprint/ciborium-ll-88ab61518aa1cb64/dep-lib-ciborium_ll","checksum":false}}],"rustflags":[],"config":2069994364910194474,"compile_kind":0}