P2 complete: Docker sandbox with kernel assertions + secret broker

tc-sandbox:
- SandboxSpec/SandboxDriver + DockerDriver (bollard): uid 10001, cap-drop
  ALL, no-new-privileges, embedded seccomp deny profile (unshare/ptrace/
  bpf/keyctl/mount/...), read-only rootfs with tmpfs /tmp + /home/agent,
  network=none, mem/cpu/pids limits
- agent-base image: non-root, all setuid binaries stripped
- 6 kernel-level assertion tests probing from INSIDE real containers:
  uid + CapEff==0, rootfs read-only, seccomp EPERM on unshare, zero
  traffic-carrying interfaces + failed egress connect, no setuid +
  NoNewPrivs=1, lifecycle

tc-secrets:
- ChaCha20-Poly1305 envelope encryption under a FileKey (generated 0600,
  AEAD tamper detection tested); secrets table ciphertext-at-rest
- teamclaw-broker daemon: length-prefixed JSON over a unix socket; no
  protocol operation ever returns plaintext; InvokeHttp independently
  consumes the single-use execution grant against Postgres BEFORE touching
  any credential, then performs the call itself with the secret injected
- Tests over the real socket + real Postgres + a real local HTTP receiver:
  encrypted at rest, pending approval refused, approved call carries the
  bearer token exactly once, grant replay refused, non-http URLs rejected

116 Rust + 61 frontend tests + 14 E2E journeys green.

Co-Authored-By: Claude Fable 5 <[email protected]>

crates/bins/teamclaw-broker/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "teamclaw-broker"
+version = "0.1.0"
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+publish.workspace = true
+
+[dependencies]
+tc-db = { path = "../../tc-db" }
+tc-secrets = { path = "../../tc-secrets" }
+tokio = { workspace = true }
+
+[lints]
+workspace = true