feat(lib/github): OFFLINE=1 short-circuits require_github_release

Hosts that cannot reach github.com (e.g. an Iran-only egress) cannot
fetch binary releases. Previously this caused any script depending on
`require_github_release` (currently fetch.sh, alacritty.sh, several
others) to fail the entire start.sh run with a 5-minute curl timeout.

When OFFLINE=1 is set in the environment, the function now logs a
skip and returns 0, treating the dependency as satisfied
(best-effort). Callers that NEED the github binary still fail at
runtime when the binary is invoked, but the install script itself
no longer aborts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 1995parham

scripts/lib/github.sh

@@ -266,6 +266,16 @@ require_github_release() {
     local release_name=${3:?'release name is required (e.g., clash-aarch64-apple-darwin)'}
     local archive_ext=${4:-""}
 
+    # Airgapped escape hatch: when OFFLINE=1 is set, hosts that cannot
+    # reach github.com (e.g. an Iran-only egress) can still run scripts
+    # that depend on require_github_release. We log a skip and return 0
+    # so the calling script's framework treats the dependency as
+    # "satisfied (best-effort)" rather than failing the run.
+    if [[ "${OFFLINE:-0}" == "1" ]]; then
+        running "require" " github-release ${repo} ${binary_name} (skipped: OFFLINE=1)"
+        return 0
+    fi
+
     local install_dir="${HOME}/.local/bin"
     mkdir -p "${install_dir}"