feat(tools): the contract crate — allowlist, header, conformance suite

The client tools need one shared definition of what a tool may do,
and the daemon needs to enforce exactly that definition, not a
hand-copied copy of it. This crate is that definition, pure: no HTTP
client, no process — the allowlist as data, the version header as
constants, the request/response and error types, and the conformance
suite that drives any transport through the checks the contract
promises (the bearer gate, the version handshake, the allowlist's
denials, round-trips through every allowed route, one error shape).

`agent_allowed` is the whole security surface in one function:
method and path segments with `*` and `**`, exact otherwise — a
daemon's middleware asks it and nothing else, so the claw's scoping
and the tools' expectations cannot drift apart. The suite runs
against a mock router in this crate's tests and against the daemon's
real axum router in the claw's; same results is the definition of
implementing the contract.

tools/contract/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "rhema-tools-contract"
+description = "The wire contract between the rhema claw daemon and its thin client tools: routes, shapes, the agent-token allowlist, and the conformance suite"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+authors.workspace = true
+
+[dependencies]
+serde.workspace = true
+serde_json.workspace = true
+
+[dev-dependencies]
+tokio.workspace = true
+
+[lints.rust]
+unsafe_code = "forbid"
+missing_docs = "deny"