fix: generate .agents directory at setup time instead of shipping duplicates (#308)

Removes 14K+ lines of committed generated Codex skill files from git.
.agents/ is now gitignored and generated at setup time via
`bun run gen:skill-docs --host codex`. Updates CI workflow to validate
generation instead of checking committed file freshness.

Co-authored-by: cskwork <cskwork@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

setup

@@ -94,6 +94,27 @@ if [ ! -x "$BROWSE_BIN" ]; then
   exit 1
 fi
 
+# 1b. Generate .agents/ Codex skill docs if missing or stale
+# .agents/ is no longer committed — generated at setup time from .tmpl templates.
+# bun run build already does this, but we need it when NEEDS_BUILD=0 (binary is fresh
+# but .agents/ hasn't been generated yet, e.g., fresh clone).
+AGENTS_DIR="$GSTACK_DIR/.agents/skills"
+NEEDS_AGENTS_GEN=0
+if [ ! -d "$AGENTS_DIR" ]; then
+  NEEDS_AGENTS_GEN=1
+elif [ -n "$(find "$GSTACK_DIR" -maxdepth 2 -name 'SKILL.md.tmpl' -newer "$AGENTS_DIR" -print -quit 2>/dev/null)" ]; then
+  NEEDS_AGENTS_GEN=1
+fi
+
+if [ "$NEEDS_AGENTS_GEN" -eq 1 ] && [ "$NEEDS_BUILD" -eq 0 ]; then
+  echo "Generating .agents/ skill docs..."
+  (
+    cd "$GSTACK_DIR"
+    bun install --frozen-lockfile 2>/dev/null || bun install
+    bun run gen:skill-docs --host codex
+  )
+fi
+
 # 2. Ensure Playwright's Chromium is available
 if ! ensure_playwright_browser; then
   echo "Installing Playwright Chromium..."
@@ -166,7 +187,12 @@ link_codex_skill_dirs() {
   local linked=()
 
   if [ ! -d "$agents_dir" ]; then
-    echo "  warning: no .agents/skills/ directory found — run 'bun run build' first" >&2
+    echo "  Generating .agents/ skill docs..."
+    ( cd "$gstack_dir" && bun run gen:skill-docs --host codex )
+  fi
+
+  if [ ! -d "$agents_dir" ]; then
+    echo "  warning: .agents/skills/ generation failed — run 'bun run gen:skill-docs --host codex' manually" >&2
     return 1
   fi