ci(cross-platform): Linux-only for now (defer macOS/Windows) (#36)

* ci(cross-platform): gate on Linux, make macOS/Windows non-blocking

Focus CI on Linux now and defer full cross-platform support to a later
effort. The FFI is currently POSIX-only — probe.zig uses fcntl/F.GETFL
for non-blocking sockets and cli.zig uses posix.getenv — so Windows does
not compile (F is void on Windows; posix.getenv is unavailable there) and
macOS is build-only. Rather than block every PR on targets that are not
supported yet:

- Linux: gates as before (build + integration tests; continue-on-error false)
- macOS + Windows: still build for early signal, but continue-on-error true,
  so they no longer fail the workflow or gate merges.

Full Windows/macOS support (fcntl -> ioctlsocket(FIONBIO),
posix.getenv -> std.process.getEnvVarOwned, and whatever else surfaces)
is tracked for a dedicated cross-platform effort.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LvsZgNxFbeqfRmrVFNhJ8G

* ci(cross-platform): drop macOS/Windows legs (Linux-only for now)

Supersedes the continue-on-error approach in the previous commit. Job-level
continue-on-error stops the overall workflow run from failing, but the
individual macOS/Windows jobs still report conclusion=failure to the Checks
API — i.e. they keep showing red and firing failure webhooks, which is not
"defer them". Removing the legs from the matrix is the clean way to set those
expectations aside: no Windows red, no noise.

Linux is the sole platform until the dedicated cross-platform effort re-adds
macOS/Windows (Windows needs fcntl -> ioctlsocket(FIONBIO) and
posix.getenv -> std.process.getEnvVarOwned). The matrix structure is kept so
re-adding os/name there is a one-line change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LvsZgNxFbeqfRmrVFNhJ8G

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/cross-platform.yml

@@ -1,6 +1,8 @@
 # SPDX-License-Identifier: MPL-2.0
-# Cross-platform CI for Game Server Admin
-# Builds and tests on Linux, macOS, and Windows
+# CI for Game Server Admin — Linux only for now.
+# macOS and Windows are deferred to the dedicated cross-platform effort:
+# the FFI is currently POSIX-only (fcntl sockets, posix.getenv) and does
+# not compile on Windows. Re-add the matrix legs there.
 
 name: Cross-Platform Build & Test
 
@@ -19,15 +21,11 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          # Linux only for now; macOS/Windows deferred to the cross-platform
+          # effort. Kept as a matrix so re-adding os/name there is trivial.
           - os: ubuntu-latest
             name: Linux
             run-integration: true
-          - os: macos-latest
-            name: macOS
-            run-integration: false
-          - os: windows-latest
-            name: Windows
-            run-integration: false
 
     name: ${{ matrix.name }}
     runs-on: ${{ matrix.os }}