fix(fedimint): gateway/guardian follow the running bitcoin container via {{BITCOIN_HOST}}

The gateway crash-looped dialing bitcoind at host.archipelago:8332 (the
host gateway IP, where bitcoind does not listen). Root-cause fix, three
parts:

- fedimint-gateway manifest: --bitcoind-url now comes from
  $FM_BITCOIND_URL, filled by a {{BITCOIN_HOST}} derived-env — works on
  Knots, Core, or any future Bitcoin distro.
- fedimint manifest: same derived-env replaces the hardcoded
  FM_BITCOIND_URL=http://bitcoin-knots:8332 environment entry.
- orchestrator: removed the hardcoded FM_BITCOIND_URL=bitcoin-knots
  override that clobbered the derived-env, and bitcoin_host() now
  accepts any running bitcoin*/bitcoin container (excluding -ui and
  archy-* sidecars), preferring the known names in order.

Catalog regenerated + signed (nodes install from the signed catalog, so
the manifest fixes only reach them via this regen).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/fedimint/manifest.yml

@@ -21,6 +21,11 @@ app:
         template: fedimint://{{HOST_MDNS}}:8173
       - key: FM_API_URL
         template: ws://{{HOST_MDNS}}:8174
+      # Resolves to whichever bitcoin container is running (Knots/Core/future
+      # distro) instead of a hardcoded name — the guardian works on any node
+      # regardless of which Bitcoin software it runs.
+      - key: FM_BITCOIND_URL
+        template: "http://{{BITCOIN_HOST}}:8332"
     secret_env:
       - key: FM_BITCOIND_PASSWORD
         secret_file: bitcoin-rpc-password
@@ -62,7 +67,8 @@ app:
 
   environment:
     - FM_DATA_DIR=/data
-    - FM_BITCOIND_URL=http://bitcoin-knots:8332
+    # FM_BITCOIND_URL comes from derived_env ({{BITCOIN_HOST}}) above, not a
+    # hardcoded name — do not re-add it here.
     - FM_BITCOIND_USERNAME=archipelago
     - FM_BITCOIN_NETWORK=bitcoin
     - FM_BIND_P2P=0.0.0.0:8173