refactor(browser): make sessionName optional, add selector filter, deduplicate session setup

- sessionName is now optional in open/exec; skips session restore when omitted
- add selector param to open: returns outerHTML or textContent of matched element
- extract session restore logic into private setupSession() to remove duplication
- replace per-exception instanceof checks with single HttpException base class check
- embed label into InternalServerErrorException message instead of logging separately
- update MCP tool schemas and HTTP DTOs to reflect optional sessionName and new selector
- add integration tests: sessionless open/exec, selector, selector+readerMode

test/__mocks__/jsdom.ts

@@ -1,6 +1,15 @@
+const mockElement = {
+  outerHTML: '<div id="mock">mock content</div>',
+  textContent: 'mock content',
+};
+
 export class JSDOM {
   constructor(public html: string, public options?: any) {}
   get window() {
-    return { document: {} };
+    return {
+      document: {
+        querySelector: (_selector: string) => mockElement,
+      },
+    };
   }
 }

test/browser.controller.spec.ts

@@ -45,13 +45,6 @@ describe('BrowserController', () => {
       await request(app.getHttpServer()).post('/open').send({}).expect(400);
     });
 
-    it('returns 400 when sessionName is missing', async () => {
-      await request(app.getHttpServer())
-        .post('/open')
-        .send({ url: 'https://example.com' })
-        .expect(400);
-    });
-
     it('returns 400 when url is missing', async () => {
       await request(app.getHttpServer())
         .post('/open')
@@ -65,6 +58,34 @@ describe('BrowserController', () => {
         .send({ sessionName: 'no-such-session', url: 'https://example.com' })
         .expect(404);
     });
+
+    it('succeeds without a session (sessionless open)', async () => {
+      const res = await request(app.getHttpServer())
+        .post('/open')
+        .send({ url: 'https://example.com' })
+        .expect(201);
+      expect(res.body).toMatchObject({
+        url: expect.any(String),
+        title: expect.any(String),
+        content: expect.any(String),
+      });
+    });
+
+    it('returns only selector content when selector is provided', async () => {
+      const res = await request(app.getHttpServer())
+        .post('/open')
+        .send({ url: 'https://example.com', selector: '#mock' })
+        .expect(201);
+      expect(res.body.content).toBe('<div id="mock">mock content</div>');
+    });
+
+    it('returns selector text content in reader mode', async () => {
+      const res = await request(app.getHttpServer())
+        .post('/open')
+        .send({ url: 'https://example.com', selector: '#mock', readerMode: true })
+        .expect(201);
+      expect(res.body.content).toBe('mock content');
+    });
   });
 
   // ── POST /exec ─────────────────────────────────────────────────────────────
@@ -94,5 +115,13 @@ describe('BrowserController', () => {
         .send({ sessionName: 'no-such-session', code: 'return 1;' })
         .expect(404);
     });
+
+    it('succeeds without a session (sessionless exec)', async () => {
+      const res = await request(app.getHttpServer())
+        .post('/exec')
+        .send({ code: 'return 42;' })
+        .expect(201);
+      expect(res.body).toEqual({ result: 42 });
+    });
   });
 });