feat(ai): migrate gemini-cli references to antigravity-cli (agy)

Rename gemini-resume → antigravity-resume and save_gemini_session →
save_antigravity_session; update all session files from .gemini_session
to .antigravity_session and LAST_GEMINI_SESSION → LAST_ANTIGRAVITY_SESSION.
Replace gemini/gemini-cli binary calls with agy throughout superpowers,
code-resume, and the resume function. Add antigravity-ide wrapper for the
renamed IDE binary; update abbr v → antigravity-ide (VSCode-equivalent)
and update README/requirements to reflect the new tool names.

functions/superpowers.fish

@@ -1,17 +1,17 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# Toggle superpowers extension for Gemini and Claude
-function superpowers --description 'Toggle superpowers extension for Gemini and Claude'
-    set -l scope_gemini workspace
+# Toggle superpowers extension for antigravity-cli and Claude
+function superpowers --description 'Toggle superpowers extension for antigravity-cli and Claude'
+    set -l scope_agy workspace
     set -l scope_claude project
     set -l mode ""
     set -l help_text "
 Usage: superpowers [on|off] [options]
 
 Commands:
-  on       Enable superpowers for Gemini and Claude
-  off      Disable superpowers for Gemini and Claude
+  on       Enable superpowers for antigravity-cli and Claude
+  off      Disable superpowers for antigravity-cli and Claude
 
 Options:
   -g, --global    Apply settings to the user/global scope
@@ -26,7 +26,7 @@ Options:
             case off
                 set mode disable
             case -g --global
-                set scope_gemini user
+                set scope_agy user
                 set scope_claude user
             case -h --help
                 echo $help_text
@@ -40,10 +40,10 @@ Options:
         return 1
     end
 
-    echo "Setting superpowers to: $mode (Scope: Gemini=$scope_gemini, Claude=$scope_claude)..."
+    echo "Setting superpowers to: $mode (Scope: antigravity-cli=$scope_agy, Claude=$scope_claude)..."
 
-    # Execute Gemini command
-    gemini extensions $mode superpowers --scope $scope_gemini
+    # Execute antigravity-cli command
+    agy extensions $mode superpowers --scope $scope_agy
 
     # Execute Claude command
     claude plugins $mode superpowers --scope $scope_claude