agy: rewire skill from dead gemini npm CLI to Antigravity 'agy' binary

The old Google gemini CLI stopped working on this account (throwIneligibleOrProjectIdError -
needs a GOOGLE_CLOUD_PROJECT the personal account can't supply). Replace it with the
Antigravity CLI (agy, native Go binary, own auth, no project ID).

- New scripts/ask-agy.sh: plain-text output (no JSON), -p prompt-last, --model friendly
  names (Gemini 3.1 Pro (High) default for verify/review*/vision/search), --add-dir for
  file/vision reads, --dangerously-skip-permissions to avoid print-mode approval hangs.
  All modes smoke-tested (text/verify/review/search).
- scripts/ask-gemini.sh: deprecated shim -> exec ask-agy.sh (back-compat).
- SKILL.md: rewired header/flags/models/auth/availability/reference to agy.
- ask-grok.sh: xsearch fallback now execs ask-agy.sh (was the dead gemini).
- identity.json (local, gitignored): agy block added, gemini marked retired.

Authoritative flags sourced from 'agy --help' (web docs are JS SPAs, unreadable by
fetch tools; grok fetch/search timed out).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.claude/skills/grok/scripts/ask-grok.sh

@@ -238,12 +238,12 @@ for ln in sys.stdin:
     if e.get("type")=="text": t.append(e.get("data",""))
 print("".join(t).strip())' < "$OUT")"
     if [ "$GRC" -eq 0 ] && [ -n "$ans" ]; then printf '%s\n' "$ans"; exit 0; fi
-    echo "[$SELF] grok xsearch did not finish (rc=$GRC) -> falling back to gemini search" >&2
-    _logerr "grok xsearch incomplete (rc=$GRC); auto-fell back to gemini" --context "mode=xsearch"
-    GEM="$REPO_ROOT/.claude/skills/agy/scripts/ask-gemini.sh"
-    if [ -f "$GEM" ]; then echo "[grok xsearch timed out -> answered via gemini search]"; exec bash "$GEM" search "$Q"; fi
+    echo "[$SELF] grok xsearch did not finish (rc=$GRC) -> falling back to agy search" >&2
+    _logerr "grok xsearch incomplete (rc=$GRC); auto-fell back to agy" --context "mode=xsearch"
+    GEM="$REPO_ROOT/.claude/skills/agy/scripts/ask-agy.sh"
+    if [ -f "$GEM" ]; then echo "[grok xsearch timed out -> answered via agy search]"; exec bash "$GEM" search "$Q"; fi
     [ -n "$ans" ] && { printf '%s\n' "$ans"; exit 0; }   # last resort: whatever partial streamed
-    echo "[$SELF] no result (grok timed out; gemini fallback unavailable)" >&2; exit 1
+    echo "[$SELF] no result (grok timed out; agy fallback unavailable)" >&2; exit 1
     ;;
   review|file)
     [ -z "${1:-}" ] && { echo "usage: $SELF review <file-path> [instructions]" >&2; exit 2; }