feat: Use incremental port assignment (like Vite) instead of random OS-assigned ports #10357

Description

When starting multiple OpenCode web servers and the default port 4096 is already in use, the server currently falls back to a random OS-assigned port (e.g., 55651). This makes it difficult to predict which port the server will use.

Expected Behavior

The server should try incremental ports (4096, 4097, 4098, etc.) similar to how Vite handles port conflicts. This provides a predictable port sequence and better developer experience.

Current Behavior

• First server: Port 4096 ✓
• Second server: Random port (e.g., 55651) ✗

Proposed Solution

When port is occupied, try incremental ports up to 10 attempts before falling back to OS-assigned port:

• First server: Port 4096
• Second server: Port 4097
• Third server: Port 4098
• etc.

This should work for both default port (4096) and custom ports specified via --port flag.

Category

Missing standard behavior - improves UX to match common dev server patterns (Vite, Next.js, etc.)