fix(doctor): handle unparseable version + empty health body

Three issues raised by code-quality reviewer on b65201b:

1. semverCompare returned 0 for unparseable input, causing fromSupported=true
   and kind=noop for an install with unreadable package.json. Now treats
   unparseable currentVersion as fresh_install candidate.
2. mockHealth: { status: 200, body: null } routed to fix_oauth (because
   health.body?.auth?.ok was undefined → falsy). 200 with empty body is
   server-broken, not OAuth-broken; now routes to fix_service.
3. Removed unused KIND_ENUM declaration (dead code).

Two regression tests added.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test-features.mjs

@@ -639,6 +639,22 @@ test("doctor service down → fix_service kind", async () => {
   assert.equal(result.next_action.kind, "fix_service");
 });
 
+test("doctor unparseable version → fresh_install", async () => {
+  const result = await runDoctor({ skipNetwork: true, mockVersion: "garbage", mockLatest: "v3.14.0" });
+  assert.equal(result.from_version_supported, false);
+  assert.equal(result.next_action.kind, "fresh_install");
+});
+
+test("doctor empty health body → fix_service (not fix_oauth)", async () => {
+  const result = await runDoctor({
+    skipNetwork: false,
+    mockVersion: "v3.10.0",
+    mockLatest: "v3.14.0",
+    mockHealth: { status: 200, body: null }
+  });
+  assert.equal(result.next_action.kind, "fix_service");
+});
+
 // ── Cleanup ──
 closeDb();