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/getrandom-77f4a1e3527e4689/invoked.timestamp

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+This file has an mtime of when this was started.

target/debug/.fingerprint/getrandom-77f4a1e3527e4689/lib-getrandom

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+097de772f262d324

target/debug/.fingerprint/getrandom-77f4a1e3527e4689/lib-getrandom.json

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+{"rustc":1100337564441796057,"features":"[\"std\"]","declared_features":"[\"compiler_builtins\", \"core\", \"custom\", \"js\", \"js-sys\", \"linux_disable_fallback\", \"rdrand\", \"rustc-dep-of-std\", \"std\", \"test-in-browser\", \"wasm-bindgen\"]","target":16244099637825074703,"profile":15657897354478470176,"path":3910037456269710281,"deps":[[7667230146095136825,"cfg_if",false,8167686646248572737],[17159683253194042242,"libc",false,9010325384394673773]],"local":[{"CheckDepInfo":{"dep_info":"debug/.fingerprint/getrandom-77f4a1e3527e4689/dep-lib-getrandom","checksum":false}}],"rustflags":[],"config":2069994364910194474,"compile_kind":0}