feat(coordinator): add local development dashboard with service status

[Labi-Joy]

Closes #325.

Adds a single-page web dashboard, served by the coordinator at http://localhost:8080/, that shows live status of every local service: the Soroban container, the three MPC nodes, the coordinator itself, and the Soroban poker_table contract deployment. The page polls /api/health every 5 seconds and renders the result into per-service cards with a clear ok / disconnected / not-configured pill.

What landed

services/coordinator/src/main.rs extends HealthResponse with a contract_deployment field (configured: bool, contract_id: String) so the dashboard can render contract deployment status without a second endpoint. configured is true when SorobanConfig::is_configured() holds (contract id set and signer not the test placeholder); the contract id is exposed so the developer can copy it and verify on-chain. Adds GET / as a new route that returns the dashboard page.

services/coordinator/src/dashboard.rs (new): tiny axum handler that returns the embedded HTML. The page is included at compile time via include_str! so no extra static-asset deployment step is required.

services/coordinator/src/dashboard.html (new): vanilla HTML + CSS + JS, no build step. Polls /api/health, renders one card per service (coordinator, soroban-rpc, three mpc-nodes, contract deployment), surfaces uptime, active MPC sessions, maintenance mode, and the contract id alongside a status pill, and shows an error banner when the coordinator becomes unreachable so the dashboard reflects local stack issues immediately.

The dashboard reads only public state already exposed by /api/health and the coordinator binary, so no new env vars, dependencies, or deploy steps are needed; it works against any coordinator instance.

Note on cargo check and upstream state

cargo check -p coordinator against the freshly fetched upstream/main (commit aec9538) currently fails with 48 compile errors that are unrelated to this PR. A quick sampling: error[E0432]: unresolved import 'utoipa', error[E0432]: unresolved import 'utoipa_swagger_ui', error[E0432]: unresolved import 'crate::api_keys', error[E0609]: no field 'mpc_client' on type 'AppState', error[E0560]: struct 'HealthResponse' has no field 'maintenance_mode' (the populator at the bottom of health() references a field that no longer exists on the struct). These look like the tail of an in-flight refactor that landed on main without the dependent crates / modules being introduced.

Applying this PR on top of upstream/main leaves the error count at exactly the same number (48), i.e. the dashboard module does not introduce any new errors and is internally coherent (the new HealthResponse.contract_deployment field is added to the struct, the components(schemas(...)) list, and the health() populator together). I confirmed this by running cargo check -p coordinator on aec9538 directly and on aec9538 + this PR.

Once upstream main compiles again, I can rebase and confirm a clean check.

How to verify locally

docker compose up -d soroban mpc-node-0 mpc-node-1 mpc-node-2
cargo run -p coordinator
# in another shell
open http://localhost:8080/

Cards should appear within a few seconds and refresh every 5 seconds.

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