test: add deploy coverage test (orphan-read invariant)

[AquiGorka]

Why this PR exists

Mirrors the test landed in moonlight-pay PR #27 to catch the orphan-read class of bug across the other 3 Moonlight frontends:

• Frontend reads `config.X` (via a runtime config object).
• Deploy.yml is supposed to write `X` into the bundled `public/config.js`.
• If a dev adds a new field to the config interface but forgets to wire it in deploy.yml, the field is silently `undefined` in production. No error, no warning — the feature is just dead.

The original moonlight-pay incident: `adminWallets` had been read by `isAdmin()` since the admin route shipped, but no part of deploy.yml wrote it. The `/#/admin` page was unreachable from day one.

This PR closes the gap on `network-dashboard`.

How it works

`src/lib/config_deploy_test.ts` is a pure static check (no build, no env vars, no runtime):

1. Extracts the keys declared on `interface DashboardConfig` in `src/lib/config.ts`.
2. Extracts the keys written by each `Generate ... config` step in `.github/workflows/deploy.yml`, between the `Generate {production,mainnet} config` and `Build production bundle` markers. (This repo's deploy uses `deno eval` rather than a heredoc, but the same line-level regex picks up the JS object keys.)
3. Fails if any source-side key is missing, unless it's in the per-network `DEFAULT_OK` allowlist (for keys whose source-side default is intentionally correct for that network).

Two assertions: one for testnet (`Generate production config`), one for mainnet (`Generate mainnet config`).

Per-network audit

4 keys declared on `DashboardConfig` (`environment`, `stellarNetwork`, `rpcUrl`, `councilPlatformUrl`).

• testnet: heredoc writes all 4. `DEFAULT_OK.testnet = ∅`.
• mainnet: heredoc writes all 4. `DEFAULT_OK.mainnet = ∅`.

No hard orphans, no soft orphans.

Negative-test evidence

Before opening: removed `rpcUrl: Deno.env.get('RPC_URL'),` from the `Generate production config` step → `deno task test` reported failure with `rpcUrl` missing from testnet deploy. Restored the line → green.

```
deploy.yml writes every DashboardConfig key on testnet (or it's in DEFAULT_OK) ...
[Diff] Actual / Expected

• [

• "rpcUrl",
  

• ]

• []
  FAILED | 1 passed | 1 failed
  ```

Test plan

• `deno task test` green locally (30 passed total)
• `deno fmt --check` clean
• `deno lint` clean
• `deno task build` clean
• CI green