[docs] add banner indicating v2 vs v3 toggle (#1375)

# why

Users don't know about the v2/v3 version toggle in the docs navigation.

# what changed

Added a banner at the top of the v3 docs pages to help users easily
discover Stagehand Python (v2).

# test plan
n/a




<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Added a reusable banner to the top of all v3 docs pages to highlight the
Stagehand Python (v2) option. Improves discoverability of the v2/v3
toggle and reduces confusion.

- **New Features**
- Added V3Banner MDX snippet linking to “/v2/first-steps/introduction”.
- Imported and rendered the banner across v3 Basics, Best Practices,
Configuration, First Steps, Integrations, Migrations, and References
pages.
- Minor metadata/formatting updates in v2 docs (e.g., User Data
frontmatter) for consistency.

<sup>Written for commit 515a13d.
Summary will update automatically on new commits.</sup>

<!-- End of auto-generated description by cubic. -->

Author: shrey150

packages/docs/snippets/v3-banner.mdx

@@ -0,0 +1,13 @@
+export const V3Banner = () => (
+  <div className="mb-5 flex items-center justify-between gap-4 rounded-md border border-zinc-700/50 bg-zinc-800/50 px-4 py-3 text-sm">
+    <span className="text-zinc-400">
+      🐍&nbsp;&nbsp;Looking for <strong className="text-zinc-200">Stagehand in Python</strong>?
+    </span>
+    <a 
+      href="/v2/first-steps/introduction" 
+      className="text-zinc-400 hover:text-zinc-200 transition-colors no-underline text-xs"
+    >
+      Switch to v2 →
+    </a>
+  </div>
+);

packages/docs/v2/best-practices/user-data.mdx

@@ -1,3 +1,8 @@
+---
+title: User Data Directory
+sidebarTitle: User Data
+description: Persist browser data between sessions
+---
 
 ### User Data Directory
 

packages/docs/v3/basics/act.mdx

@@ -2,6 +2,10 @@
 title: Act
 description: 'Interact with a web page'
 ---
+import { V3Banner } from '/snippets/v3-banner.mdx';
+
+<V3Banner />
+
 
 ## What is `act()`?
 ``` typescript

packages/docs/v3/basics/agent.mdx

@@ -2,6 +2,10 @@
 title: Agent
 description: 'Automate complex workflows with AI powered browser agents'
 ---
+import { V3Banner } from '/snippets/v3-banner.mdx';
+
+<V3Banner />
+
 
 ## What is `agent()?`
 

packages/docs/v3/basics/evals.mdx

@@ -3,6 +3,10 @@ title: Evaluations & Metrics
 sidebarTitle: Evals
 description: Monitor performance, optimize costs, and evaluate LLM effectiveness
 ---
+import { V3Banner } from '/snippets/v3-banner.mdx';
+
+<V3Banner />
+
 
 Evaluations help you understand how well your automation performs, which models work best for your use cases, and how to optimize for cost and reliability. This guide covers both monitoring your own workflows and running comprehensive evaluations.
 

packages/docs/v3/basics/extract.mdx

@@ -2,6 +2,10 @@
 title: Extract
 description: Extract structured data from a webpage
 ---
+import { V3Banner } from '/snippets/v3-banner.mdx';
+
+<V3Banner />
+
 
 ## What is `extract()`?
 

packages/docs/v3/basics/observe.mdx

@@ -3,6 +3,10 @@ title: Observe
 sidebarTitle: Observe
 description: 'Discover and plan executable actions on any web page'
 ---
+import { V3Banner } from '/snippets/v3-banner.mdx';
+
+<V3Banner />
+
 
 ## What is `observe()`?
 

packages/docs/v3/best-practices/agent-fallbacks.mdx

@@ -2,6 +2,10 @@
 title: Agent Fallbacks
 description: "A failsafe when unexpected page changes add extra steps"
 ---
+import { V3Banner } from '/snippets/v3-banner.mdx';
+
+<V3Banner />
+
 
 ## When to use
 

packages/docs/v3/best-practices/caching.mdx

@@ -2,6 +2,10 @@
 title: Caching Actions
 description: Cache actions automatically to reduce costs and improve performance
 ---
+import { V3Banner } from '/snippets/v3-banner.mdx';
+
+<V3Banner />
+
 
 Stagehand provides built-in action caching to reduce LLM inference calls and improve performance. Simply specify a `cacheDir` when initializing Stagehand, and actions are automatically cached and reused across runs.
 

packages/docs/v3/best-practices/computer-use.mdx

@@ -2,6 +2,10 @@
 title: Computer Use Agents
 description: Incorporate Computer Use APIs from Google, Anthropic, and OpenAI with one line of code in Stagehand.
 ---
+import { V3Banner } from '/snippets/v3-banner.mdx';
+
+<V3Banner />
+
 
 ## What is a Computer Use Agent?