fix(mempool): self-healing nginx backend proxy (v3.0.1) + gate timeout

The frontend nginx used a literal proxy_pass host with no resolver, so it
pinned mempool-api's IP at worker startup. When the backend restarts (gate,
OTA, crash, reboot re-IPAM) podman reassigns its IP and nginx keeps proxying
to the dead one -> /api hangs, websocket 502s, UI shows 'offline' until a
manual nginx reload. Same stale-upstream-IP class as the netbird 502.

Fix: mempool-frontend:v3.0.1 rewrites the generated nginx-mempool.conf to
re-resolve the backend per-request via 'resolver' + a variable proxy_pass.
Resolver address is read from /etc/resolv.conf (podman aardvark-dns answers
on the network gateway, not Docker's 127.0.0.11). Per-location path mapping
preserved (ws -> '/', /api/v1 identity via no-URI, /api/ -> /api/v1/ rewrite).
Proven on .228: backend IP change now auto-recovers with no reload; the
literal-host control still 502s. Migrated the manifest off the retired
tx1138 registry to vps2.

Also: mempool.bats #74 waited only 180s post-restart (the slow path) and
called an undefined 'fail' helper (status 127). Bumped to 300s to match the
passing parity probes and emit a real failure instead.

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

apps/archy-mempool-web/manifest.yml

@@ -1,12 +1,12 @@
 app:
   id: archy-mempool-web
   name: Mempool Web
-  version: 3.0.0
+  version: 3.0.1
   description: Frontend web UI for mempool explorer.
   container_name: mempool
 
   container:
-    image: git.tx1138.com/lfg2025/mempool-frontend:v3.0.0
+    image: 146.59.87.168:3000/lfg2025/mempool-frontend:v3.0.1
     pull_policy: if-not-present
     network: archy-net
 

apps/mempool/manifest.yml

@@ -5,7 +5,7 @@ app:
   description: Bitcoin mempool and blockchain explorer. Real-time transaction and block visualization.
   
   container:
-    image: 146.59.87.168:3000/lfg2025/mempool-frontend:v3.0.0
+    image: 146.59.87.168:3000/lfg2025/mempool-frontend:v3.0.1
     image_signature: cosign://...
     pull_policy: if-not-present