Fix Week 1 Claude Code install commands (#18)

- macOS: brew install claude-code -> brew install --cask claude-code (cask is required)
- Linux/WSL: install-cli endpoint -> install.sh endpoint (the old URL is no longer canonical)
- Add PowerShell install path for native Windows users
- Point the anchor link at code.claude.com/docs/en/overview instead of the legacy claude.ai/claude-code URL

Fixes #17

Author: neuromechanist

courses/agentic-research/week-01.md

@@ -402,26 +402,40 @@ If all of these work, you are ready for Week 2.
 ## Before Next Session
 
 !!! note "Install Claude Code"
-    Before Week 2, install [Claude Code](https://claude.ai/claude-code):
+    Before Week 2, install [Claude Code](https://code.claude.com/docs/en/overview):
 
     === "macOS"
 
+        Native install (recommended, auto-updates):
+
+        ```bash
+        curl -fsSL https://claude.ai/install.sh | bash
+        ```
+
+        Or via Homebrew:
+
         ```bash
-        brew install claude-code
+        brew install --cask claude-code
         ```
 
     === "Linux"
 
         ```bash
-        curl -fsSL https://claude.ai/install-cli | sh
+        curl -fsSL https://claude.ai/install.sh | bash
         ```
 
     === "Windows"
 
         In your WSL Ubuntu terminal:
 
         ```bash
-        curl -fsSL https://claude.ai/install-cli | sh
+        curl -fsSL https://claude.ai/install.sh | bash
+        ```
+
+        Or directly in PowerShell (requires [Git for Windows](https://git-scm.com/downloads/win)):
+
+        ```powershell
+        irm https://claude.ai/install.ps1 | iex
         ```
 
     Verify: