fix(fedimint): run fmcd with seccomp=unconfined so its DHT can start (#7)

fmcd crash-looped "Operation not permitted (os error 1)" on .116 (kernel
6.12.74): the default rootless seccomp profile blocks a syscall its Mainline-DHT
/ iroh transport needs, so the REST API never came up (:8178 → HTTP 000) and
federations couldn't be joined. Verified: with seccomp=unconfined fmcd boots and
answers /v2/* (HTTP 401 instead of dead). fmcd works on other nodes, so this is
kernel/seccomp-specific — but the relaxation is safe for an outbound-networking
daemon and harmless where not needed.

- new `security.seccomp_unconfined` manifest flag (SecurityPolicy);
- libpod backend sets `seccomp_profile_path: "unconfined"` (== --security-opt
  seccomp=unconfined); quadlet backend emits `SeccompProfile=unconfined`;
- enabled in apps/fedimint-clientd/manifest.yml.

NOTE: manifests live on-disk at /opt/archipelago/apps/<id>/manifest.yml, so the
node needs the updated manifest deployed + the fmcd container recreated to apply.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

core/container/src/manifest.rs

@@ -228,6 +228,13 @@ pub struct SecurityPolicy {
     pub network_policy: String,
     #[serde(default)]
     pub apparmor_profile: Option<String>,
+    /// Run the container with `seccomp=unconfined`. Needed by daemons whose
+    /// networking uses syscalls blocked by the default rootless seccomp profile
+    /// on some kernels — e.g. fmcd's Mainline-DHT/iroh transport, which otherwise
+    /// crash-loops with "Operation not permitted (os error 1)" (#7). Opt-in only;
+    /// a mild relaxation, so reserve it for apps that genuinely need it.
+    #[serde(default)]
+    pub seccomp_unconfined: bool,
 }
 
 fn default_true() -> bool {