Add standalone host-agent binaries to releases

Issue: HOST_AGENT.md documented downloading pulse-host-agent binaries
from GitHub releases, but those assets didn't exist. Only tarballs were
available, making manual installation unnecessarily complex.

Changes:
- Copy standalone host-agent binaries (all architectures) to release/
  directory alongside sensor-proxy binaries
- Include host-agent binaries in checksum generation
- Update HOST_AGENT.md to clarify available architectures
- Retroactively uploaded missing binaries to v4.26.1

This enables air-gapped and manual installations without requiring an
already-running Pulse server to download from.

docs/HOST_AGENT.md

@@ -74,15 +74,20 @@ Prefer to take full control or working in air-gapped environments? You can still
 #### Linux (systemd)
 
 ```bash
+# Download the binary for your architecture
 sudo curl -fsSL https://github.com/rcourtman/Pulse/releases/latest/download/pulse-host-agent-linux-amd64 \
   -o /usr/local/bin/pulse-host-agent
 sudo chmod +x /usr/local/bin/pulse-host-agent
+
+# Run the agent
 sudo /usr/local/bin/pulse-host-agent \
   --url http://pulse.example.local:7655 \
   --token <api-token> \
   --interval 30s
 ```
 
+Available Linux architectures: `pulse-host-agent-linux-amd64`, `pulse-host-agent-linux-arm64`, `pulse-host-agent-linux-armv7`
+
 For persistence, drop a systemd unit (e.g. `/etc/systemd/system/pulse-host-agent.service`) referencing the same command and enable it with `systemctl enable --now pulse-host-agent`.
 
 #### macOS (launchd)