Fix linux-musl platform ID string format to match PlatformId enum (#899)

The get_platform_id() function was generating "linux-arm64-musl" but the
PlatformId enum expects "linux-musl-arm64". This caused a ValueError on
musl-based Linux systems (e.g., Alpine Linux on arm64).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: mhaynie <mhaynie@pazer.us>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

src/solidlsp/ls_utils.py

@@ -324,7 +324,8 @@ class PlatformUtils:
             if system == "Linux" and bitness == "64bit":
                 libc = platform.libc_ver()[0]
                 if libc != "glibc":
-                    platform_id += "-" + libc
+                    # Format: linux-musl-arch (e.g., linux-musl-arm64)
+                    platform_id = f"{system_map[system]}-{libc}-{machine_map[machine]}"
             return PlatformId(platform_id)
         else:
             raise SolidLSPException(f"Unknown platform: {system=}, {machine=}, {bitness=}")