docs(github-auth): document headless gh auth login --with-token hang + hosts.yml fallback

On keyring-less headless Linux (VPS, containers, no dbus session),
'gh auth login --with-token' can block indefinitely waiting on a
secret-service keyring -- even with --insecure-storage, with no output.
Hit live on a headless x86_64 VPS (gh 2.97.0): the documented device
flow succeeded up to the token, then --with-token hung twice.

- Add a timeout guard to the device-flow polling loop so the hang is
  detected instead of silently stalling the login.
- Document the proven fallback: write ~/.config/gh/hosts.yml directly
  (chmod 600) and run 'gh auth setup-git' -- both read the file store
  without touching the keyring.

skills/github/github-auth/SKILL.md

@@ -195,7 +195,10 @@ while true; do
   case "$POLL" in
     *access_token*)
       # Never echo the token; pipe it straight into gh.
-      echo "$POLL" | sed 's/.*"access_token":"\([^"]*\)".*/\1/' | gh auth login --with-token
+      # timeout guards the headless-keyring hang (see pitfall below) —
+      # on exit 124, fall back to writing ~/.config/gh/hosts.yml directly.
+      echo "$POLL" | sed 's/.*"access_token":"\([^"]*\)".*/\1/' | timeout 20 gh auth login --with-token \
+        || { echo "WITH_TOKEN_HUNG_OR_FAILED — use the hosts.yml fallback below"; exit 1; }
       gh auth setup-git
       gh auth status
       echo "LOGIN_COMPLETE"; break ;;
@@ -210,6 +213,29 @@ done
 
 Note: on Windows winget installs, gh lands at `/c/Program Files/GitHub CLI` — add it to PATH in the same shell: `export PATH="$PATH:/c/Program Files/GitHub CLI"`.
 
+> **PITFALL (headless Linux): `gh auth login --with-token` can hang forever.**
+> On keyring-less/headless boxes (VPS, containers, no dbus session), gh's
+> credential storage may block indefinitely waiting on a secret-service
+> keyring — even with `--insecure-storage`, and with no output. If the
+> command doesn't return within ~20s (wrap it in `timeout 20 …` to detect
+> this), skip gh's login machinery and write the credential store directly:
+>
+> ```bash
+> # $TOKEN = the access token from the device flow above (never echo it)
+> mkdir -p ~/.config/gh
+> LOGIN=$(curl -s -H "Authorization: token $TOKEN" https://api.github.com/user \
+>   | sed 's/.*"login": *"\([^"]*\)".*/\1/')
+> printf 'github.com:\n    users:\n        %s:\n            oauth_token: %s\n    git_protocol: https\n    oauth_token: %s\n    user: %s\n' \
+>   "$LOGIN" "$TOKEN" "$TOKEN" "$LOGIN" > ~/.config/gh/hosts.yml
+> chmod 600 ~/.config/gh/hosts.yml
+> gh auth status          # reads hosts.yml directly — verifies without the keyring
+> gh auth setup-git       # wires the git credential helper (does not hang)
+> ```
+>
+> `gh auth status` and `setup-git` read the file store without touching the
+> keyring, so they work immediately. Proven on a headless x86_64 VPS
+> (gh 2.97.0, Aug 2026) after `--with-token` hung twice.
+
 ### Token-Based Login (Headless / SSH Servers)
 
 ```bash
@@ -219,6 +245,8 @@ echo "<THEIR_TOKEN>" | gh auth login --with-token
 gh auth setup-git
 ```
 
+If `--with-token` hangs here, use the hosts.yml fallback from the pitfall above.
+
 ### Verify
 
 ```bash