feat: federation panel + Dart SDK federation methods (0.70.0)

A new 'Föderation' destination (primary side) lists connected
satellites — name, region, version, wire version, advertised
capabilities — and adds them in one step: 'Add satellite' issues a
single-use bootstrap token bundled with the primary CA as a
ready-to-paste satellite config (the bundled CA makes the first
connect tamper-proof). Localized EN + DE, in-app help doc. Uses the
new HubService.listSatellites / issueSatelliteToken wrapping the
SDK's federation methods.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

assets/docs/federation.md

@@ -0,0 +1,43 @@
+# Federation
+
+Federation lets one hub (the **primary**) run capabilities on
+another hub (a **satellite**) — for example to reach a GPU box or to
+keep data inside a specific location. A flow step opts in with an
+`on:` selector; everything else stays exactly like a local step.
+
+This panel is the **primary** side: it shows the satellites currently
+connected and lets you enrol new ones.
+
+## Add a satellite
+
+1. Press **Add satellite** and give it a name (e.g. `satellite-a`).
+2. The hub issues a single-use **bootstrap token** and bundles its
+   **CA certificate**. Copy the shown config into the satellite's
+   `config.yaml` (one paste) and export the token as
+   `FAI_BOOTSTRAP_TOKEN`.
+3. Start the satellite. It dials the primary, the CA pin makes the
+   first connect tamper-proof, and the primary signs it a short-lived
+   certificate. It then appears in this list.
+
+## How it stays secure
+
+- The satellite **dials outbound** — no inbound firewall change.
+- Every connection is **mTLS**. The first connect is verified against
+  the bundled CA; later connects authenticate with the satellite's
+  own certificate (no token needed).
+- The satellite resolves and runs the capability in **its own
+  sandbox** — only inputs cross the wire, never code.
+- Each cross-hub call is recorded on both sides (`dispatched_to`), so
+  the audit trail and replay determinism survive federation.
+
+## Using a satellite in a flow
+
+Add an `on:` selector to a step:
+
+```yaml
+- id: extract
+  use: text.extract@^1
+  on: region=berlin        # or pin=satellite-a, auto:healthiest, auto:lowest_rtt
+  with:
+    input: $inputs.doc
+```