UDP socket binding fails on Windows when dual-stack/VPN active (wsasendto: invalid context)

### Describe the Bug

When running `olm` on Windows alongside a secondary system VPN (such as Proton VPN), the daemon fails to establish a P2P holepunch or UDP connection.

During socket initialization, the Go network stack selects a local **IPv6 source address** (e.g., from a virtual/tunnel adapter) to target an **IPv4 destination address** (the exit node). This causes `wsasendto` on Windows to fail with `The requested address is not valid in its context.`.

Even with `"disableHolepunch": true` set in the configuration, initial UDP holepunch packets still attempt to bind and send via the wrong interface, causing connection failures.

### Environment

### Environment
- **OS:** Windows 10 / 11
- **Olm Version:** 1.8.2
- **Co-existing Software:** Proton VPN (or other Wintun / Dual-Stack VPN interfaces)

### To Reproduce

### Steps to Reproduce
1. Start Proton VPN (or any similar Wintun/BFE-based VPN) on Windows.
2. Launch `olm` daemon.
3. Observe `HOLEPUNCH_MISSING` and `wsasendto` socket error logs.

### Relevant Logs
```text
INFO: Created shared UDP socket on port 61377 (refcount: 2)
INFO: Starting hole punch for 1 exit nodes
WARN: Failed to send initial hole punch to gate.example.com: failed to write to UDP: write udp [fd00::1234:5678]:61377->203.0.113.10:21820: wsasendto: The requested address is not valid in its context.
ERROR: Olm error (code: HOLEPUNCH_MISSING): Unable to coordinate client P2P connection. Please ensure your client can reach the server on UDP port 21820 and try registering again.

### Expected Behavior

1. IPv4 Binding Option / Fix: Provide an option in config.json (or automatically handle in code) to force binding listeners/sockets to IPv4 (0.0.0.0) or filter out IPv6 source IPs when targeting IPv4 endpoints.
2. Strict disableHolepunch Handling: Ensure that setting "disableHolepunch": true completely suppresses initial UDP holepunch attempts to prevent socket binding errors when P2P UDP is blocked/incompatible with host adapters.