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_core-54f81c8505f29549/output

@@ -0,0 +1,11 @@
+cargo:rerun-if-changed=build.rs
+cargo:rustc-check-cfg=cfg(if_docsrs_then_no_serde_core)
+cargo:rustc-check-cfg=cfg(no_core_cstr)
+cargo:rustc-check-cfg=cfg(no_core_error)
+cargo:rustc-check-cfg=cfg(no_core_net)
+cargo:rustc-check-cfg=cfg(no_core_num_saturating)
+cargo:rustc-check-cfg=cfg(no_diagnostic_namespace)
+cargo:rustc-check-cfg=cfg(no_serde_derive)
+cargo:rustc-check-cfg=cfg(no_std_atomic)
+cargo:rustc-check-cfg=cfg(no_std_atomic64)
+cargo:rustc-check-cfg=cfg(no_target_has_atomic)