feat: add Devin CLI support

Devin CLI's `devin plugins install obra/superpowers` fails today because the
repo has no `.devin-plugin/plugin.json` manifest. Add the manifest (skills are
auto-discovered from the co-located skills/ directory), a Devin tool mapping
linked from using-superpowers' Platform Adaptation section, a README install
section, version tracking in .version-bump.json, a Codex-sync exclude for the
new dotdir, and a CI-safe test mirroring the kimi/antigravity test style.

Bootstrap rides Devin's native skill surfacing: every installed skill's
name + description is injected into the system prompt at session start with a
standing instruction to invoke matching skills via the native skill tool.
Acceptance test ("Let's make a react todo list") passes in a clean session:
using-superpowers and brainstorming auto-trigger before any code is written.

tests/devin/test-devin-plugin.sh

@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+# Validate the Devin CLI integration. `devin plugins install obra/superpowers`
+# reads `.devin-plugin/plugin.json` and auto-discovers the co-located `skills/`
+# directory; Devin CLI surfaces every installed skill's name + description in
+# the system prompt at session start and invokes them via its native `skill`
+# tool, so there is no hook or injector scaffold to test. What IS Devin-specific
+# is the manifest and the tool mapping — subagent dispatch via run_subagent
+# profiles and task tracking via todo_write — and SKILL.md pointing at it.
+#
+# Mirrors tests/kimi/test-plugin-manifest.sh (manifest) and
+# tests/antigravity/test-antigravity-tools.sh (mapping). CI-safe: does not
+# require `devin` installed.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/../.." && pwd)"
+
+MANIFEST="$REPO_ROOT/.devin-plugin/plugin.json"
+MAPPING="$REPO_ROOT/skills/using-superpowers/references/devin-tools.md"
+SKILL="$REPO_ROOT/skills/using-superpowers/SKILL.md"
+
+fail() { echo "FAIL: $*" >&2; exit 1; }
+
+echo "test-devin-plugin: checking Devin CLI manifest and tool mapping"
+
+# --- Manifest is valid and matches the repo version -------------------------
+[ -f "$MANIFEST" ] || fail "manifest missing at $MANIFEST"
+
+python3 - "$MANIFEST" <<'PY'
+import json
+import sys
+from pathlib import Path
+
+manifest_path = Path(sys.argv[1])
+manifest = json.loads(manifest_path.read_text(encoding="utf-8"))
+repo_root = manifest_path.parents[1]
+
+if manifest.get("name") != "superpowers":
+    raise AssertionError(f"plugin name: expected 'superpowers', got {manifest.get('name')!r}")
+
+package = json.loads((repo_root / "package.json").read_text(encoding="utf-8"))
+if manifest.get("version") != package.get("version"):
+    raise AssertionError(
+        f"manifest version {manifest.get('version')!r} != package.json version {package.get('version')!r}"
+    )
+
+# Devin CLI plugins carry skills only (auto-discovered from ./skills/); the
+# manifest supports metadata + dependency lists, nothing executable.
+unsupported = ["skills", "hooks", "commands", "sessionStart", "contextFileName", "inject"]
+present = sorted(field for field in unsupported if field in manifest)
+if present:
+    raise AssertionError("unsupported Devin manifest fields present: " + ", ".join(present))
+
+version_config = json.loads((repo_root / ".version-bump.json").read_text(encoding="utf-8"))
+entries = version_config.get("files")
+if not isinstance(entries, list) or not any(
+    entry.get("path") == ".devin-plugin/plugin.json" and entry.get("field") == "version"
+    for entry in entries
+    if isinstance(entry, dict)
+):
+    raise AssertionError(".version-bump.json must update .devin-plugin/plugin.json version")
+
+print("Devin plugin manifest looks good")
+PY
+
+# --- Mapping exists ----------------------------------------------------------
+[ -f "$MAPPING" ] || fail "tool mapping missing at $MAPPING"
+
+# --- Core action→tool mappings are documented --------------------------------
+for tool in skill run_subagent todo_write ask_user_question; do
+  grep -q "$tool" "$MAPPING" \
+    || fail "mapping does not document the '$tool' tool"
+done
+
+# --- Subagents use the built-in profiles --------------------------------------
+grep -q 'subagent_general' "$MAPPING" \
+  || fail "mapping does not document the 'subagent_general' profile"
+grep -q 'subagent_explore' "$MAPPING" \
+  || fail "mapping does not document the 'subagent_explore' profile"
+
+# --- SKILL.md Platform Adaptation links the mapping ---------------------------
+grep -q "devin-tools.md" "$SKILL" \
+  || fail "SKILL.md Platform Adaptation does not reference devin-tools.md"
+
+echo "PASS: Devin CLI plugin valid (manifest, tool mapping, SKILL.md link)"