fix(antigravity): correct skills path + deterministic SKILL.md

Antigravity moved its skill directories: global skills now load from
~/.gemini/config/skills/ and project skills from <project>/.agents/skills/
(the old ~/.gemini/antigravity/skills/ is stale). Confirmed against Google's
Antigravity Skills docs.

- tools.json: antigravity → skill-md format, new user+project dests, scope
  user+project (keeps the `agency-` slug prefix for namespacing).
- convert.sh: emit standard Agent-Skills frontmatter only (name + description);
  drop risk/source/date_added — the date stamp made output non-deterministic,
  and it's the reason the app had kept Antigravity recognized-only. Now byte-
  identical to the osaurus skill-md shape. Removed the now-unused
  ANTIGRAVITY_DATE_ADDED constant.
- install.sh: install + detect against ~/.gemini/config/skills/.
- Docs updated.

check-tools.sh passes (tools.json / install.sh / convert.sh consistent).

Path discovery + skill-md approach by Pedro Remedios (msitarzewski/agency-agents-app#32).

Co-authored-by: Pedro Remedios <pedro.remedios@gmail.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/convert.sh

@@ -10,7 +10,7 @@
 #   ./scripts/convert.sh [--tool <name>] [--out <dir>] [--parallel] [--jobs N] [--help]
 #
 # Tools:
-#   antigravity  — Antigravity skill files (~/.gemini/antigravity/skills/)
+#   antigravity  — Antigravity skill files (~/.gemini/config/skills/)
 #   gemini-cli   — Gemini CLI subagent files (~/.gemini/agents/*.md)
 #   opencode     — OpenCode agent files (.opencode/agents/*.md)
 #   cursor       — Cursor rule files (.cursor/rules/*.mdc)
@@ -64,12 +64,6 @@ REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
 OUT_DIR="$REPO_ROOT/integrations"
 TODAY="$(date +%Y-%m-%d)"
 
-# Static date stamped into Antigravity skill frontmatter. Deliberately fixed (NOT
-# the convert-run date): a per-run TODAY made every regeneration produce different
-# bytes, which churns the gitignored output and breaks byte-reproducible rendering
-# downstream. Matches the documented example in integrations/antigravity/README.md.
-ANTIGRAVITY_DATE_ADDED="2026-03-08"
-
 # Shared helpers (get_field, get_body, slugify, ...)
 # shellcheck source=lib.sh
 . "$SCRIPT_DIR/lib.sh"
@@ -125,14 +119,14 @@ convert_antigravity() {
   outfile="$outdir/SKILL.md"
   mkdir -p "$outdir"
 
-  # Antigravity SKILL.md format mirrors community skills in ~/.gemini/antigravity/skills/
+  # Antigravity Agent-Skills SKILL.md — name + description frontmatter and the
+  # persona as the body, installed into ~/.gemini/config/skills/ (global) or
+  # <project>/.agents/skills/ (project). Standard fields only, so it stays a
+  # valid Agent-Skills skill for any host (and deterministic — no date stamp).
   cat > "$outfile" <<HEREDOC
 ---
 name: ${slug}
 description: ${description}
-risk: low
-source: community
-date_added: '${ANTIGRAVITY_DATE_ADDED}'
 ---
 ${body}
 HEREDOC

scripts/install.sh

@@ -14,7 +14,7 @@
 # Tools:
 #   claude-code  -- Copy agents to ~/.claude/agents/
 #   copilot      -- Copy agents to ~/.github/agents/ and ~/.copilot/agents/
-#   antigravity  -- Copy skills to ~/.gemini/antigravity/skills/
+#   antigravity  -- Copy skills to ~/.gemini/config/skills/
 #   gemini-cli   -- Install agents to ~/.gemini/agents/
 #   opencode     -- Copy agents to .opencode/agents/ in current directory
 #   cursor       -- Copy rules to .cursor/rules/ in current directory
@@ -363,7 +363,7 @@ check_integrations() {
 # ---------------------------------------------------------------------------
 detect_claude_code() { [[ -d "${HOME}/.claude" ]]; }
 detect_copilot()      { command -v code >/dev/null 2>&1 || [[ -d "${HOME}/.github" || -d "${HOME}/.copilot" ]]; }
-detect_antigravity()  { [[ -d "${HOME}/.gemini/antigravity/skills" ]]; }
+detect_antigravity()  { [[ -d "${HOME}/.gemini/config/skills" ]]; }
 detect_gemini_cli()   { command -v gemini >/dev/null 2>&1 || [[ -d "${HOME}/.gemini" ]]; }
 detect_cursor()       { command -v cursor >/dev/null 2>&1 || [[ -d "${HOME}/.cursor" ]]; }
 detect_opencode()     { command -v opencode >/dev/null 2>&1 || [[ -d "${HOME}/.config/opencode" ]]; }
@@ -401,7 +401,7 @@ tool_label() {
   case "$1" in
     claude-code) printf "%-14s  %s" "Claude Code"  "(claude.ai/code)"        ;;
     copilot)     printf "%-14s  %s" "Copilot"      "(~/.github + ~/.copilot)" ;;
-    antigravity) printf "%-14s  %s" "Antigravity"  "(~/.gemini/antigravity)" ;;
+    antigravity) printf "%-14s  %s" "Antigravity"  "(~/.gemini/config/skills)" ;;
     gemini-cli)  printf "%-14s  %s" "Gemini CLI"   "(~/.gemini/agents)"      ;;
     opencode)    printf "%-14s  %s" "OpenCode"     "(opencode.ai)"           ;;
     openclaw)    printf "%-14s  %s" "OpenClaw"     "(~/.openclaw/agency-agents)" ;;
@@ -720,7 +720,7 @@ install_copilot() {
 
 install_antigravity() {
   local src="$INTEGRATIONS/antigravity"
-  local dest; dest="$(resolve_dest antigravity "${HOME}/.gemini/antigravity/skills")"
+  local dest; dest="$(resolve_dest antigravity "${HOME}/.gemini/config/skills")"
   local count=0
   [[ -d "$src" ]] || { err "integrations/antigravity missing. Run convert.sh first."; return 1; }
   mkdir -p "$dest"