fix(antigravity): Add overload recovery flow

Add a Unix activation script, Antigravity-specific installer guidance,
and cross-platform recovery documentation so users can reduce the
live skill set when truncation or context overload appears.

Regenerate the canonical bundle/catalog artifacts after merging the
stale goldrush-api removal so main stays release-ready.

Refs #381

tools/scripts/tests/activate_skills_shell.test.js

@@ -0,0 +1,64 @@
+const assert = require("assert");
+const fs = require("fs");
+const os = require("os");
+const path = require("path");
+const { spawnSync } = require("child_process");
+
+const repoRoot = path.resolve(__dirname, "../..", "..");
+const scriptPath = path.join(repoRoot, "scripts", "activate-skills.sh");
+
+const root = fs.mkdtempSync(path.join(os.tmpdir(), "activate-skills-shell-"));
+const baseDir = path.join(root, "antigravity");
+const repoSkills = path.join(root, "repo-skills");
+
+function makeSkill(skillId) {
+  const skillDir = path.join(repoSkills, skillId);
+  fs.mkdirSync(skillDir, { recursive: true });
+  fs.writeFileSync(
+    path.join(skillDir, "SKILL.md"),
+    `---\nname: ${skillId}\ndescription: test skill\ncategory: testing\nrisk: safe\nsource: community\ndate_added: "2026-03-22"\n---\n`,
+    "utf8",
+  );
+}
+
+try {
+  makeSkill("brainstorming");
+  makeSkill("systematic-debugging");
+  makeSkill("custom-skill");
+
+  const result = spawnSync(
+    "bash",
+    [scriptPath, "--clear", "brainstorming", "custom-skill"],
+    {
+      cwd: repoRoot,
+      env: {
+        ...process.env,
+        AG_BASE_DIR: baseDir,
+        AG_REPO_SKILLS_DIR: repoSkills,
+        AG_PYTHON_BIN: "python3",
+      },
+      encoding: "utf8",
+    },
+  );
+
+  assert.strictEqual(result.status, 0, result.stderr || result.stdout);
+  assert.ok(
+    fs.existsSync(path.join(baseDir, "skills", "brainstorming", "SKILL.md")),
+    "brainstorming should be activated into the live skills directory",
+  );
+  assert.ok(
+    fs.existsSync(path.join(baseDir, "skills", "custom-skill", "SKILL.md")),
+    "literal safe skill ids should be activated from the library",
+  );
+  assert.ok(
+    fs.existsSync(path.join(baseDir, "skills_library", "brainstorming", "SKILL.md")),
+    "repo skills should be synced into the backing library",
+  );
+  assert.match(
+    result.stdout,
+    /Done! Antigravity skills are now activated\./,
+    "script should report successful activation",
+  );
+} finally {
+  fs.rmSync(root, { recursive: true, force: true });
+}