feat(desktop): add --port and --hostname CLI arguments for sidecar configuration

[hokonoko]

Issue for this PR

Relates to #7629, #18906, #20271

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

The OpenCode desktop app always spawns its sidecar server on a random OS-assigned port with 127.0.0.1 as hostname. The only way to override the port was the OPENCODE_PORT environment variable (compile-time or runtime). There was no way to change the hostname at all.

This PR adds --port and --hostname CLI arguments to the desktop app binary, so users can control the sidecar's listen address at launch time. This unblocks use cases like:

• Exposing the desktop server to other devices on the network (--hostname 0.0.0.0)
• Running on a predictable port for firewall rules or reverse proxies (--port 4096)
• Scripting the desktop app with a known server address

How it works:

main.rs parses CLI args via parse_cli_args_from() into a CliOptions struct (port, hostname, warnings). The struct is passed through run_with_options() → initialize(). Port/hostname overrides are applied when spawning the sidecar; invalid values produce a tracing::warn! log and fall back to defaults so the app never fails to start.

The existing run() entry point is preserved (no arguments) for #[cfg_attr(mobile, tauri::mobile_entry_point)] compatibility.

When a secondary instance is launched with --port/--hostname while a primary instance is already running, the single-instance handler logs an info message noting that these overrides are ignored.

Priority order:

1. CLI --port / --hostname (highest)
2. OPENCODE_PORT env var (port only, existing behavior)
3. Random port / 127.0.0.1 (default)

How did you verify your code works?

• cargo check --lib passes with no new warnings
• cargo test --bin opencode-desktop — 15/15 unit tests pass covering: --port N, --port=N, --hostname ADDR, --hostname=ADDR, invalid/missing values, boundary values (0, 1, 65535), combined flags, unknown flags ignored
• Manual verification of the tracing::warn output for invalid values in initialize()

Screenshots / recordings

N/A — this is a CLI argument change with no UI impact.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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