docs: improve template system documentation with context parameter clarification

- Distinguish between regular templates and partials for variable access
- Document how partials receive context via explicit parameters
- Add examples for both template types with correct syntax
- Templatize global CLAUDE.md for platform-specific shell environment sections
- Add conditional rendering for Windows, WSL, and Linux environments

CLAUDE.md

@@ -20,7 +20,14 @@ This is a **chezmoi source directory** for managing dotfiles across multiple mac
 
 **Template System:**
 - Uses Go templates with platform detection
-- Variables: `.chezmoi.os`, `.chezmoi.homeDir`, `.data.*`
+- Two types of templates with different variable access patterns:
+  - **Regular templates** (e.g., `home/dot_bashrc.tmpl`): Direct access to Chezmoi context
+    - Built-in: `.chezmoi.os`, `.chezmoi.homeDir`
+    - Custom data: `.wsl`, `.chassis`
+  - **Partials** (reusable templates in `home/.chezmoitemplates/`): Must receive context via explicit parameter
+    - Partials don't have automatic access to Chezmoi's context
+    - Context passed as parameter (commonly `data`) when calling the partial
+    - Access everything through parameter: `.data.chezmoi.os`, `.data.wsl`, `.data.chassis`
 - Conditional rendering for Windows/Linux/macOS/WSL
 
 **Secret Management:**
@@ -82,9 +89,11 @@ This is a **chezmoi source directory** for managing dotfiles across multiple mac
    - `chezmoi status` - see what's changed
 
 4. **Use templates correctly**
-   - Platform detection: `.chezmoi.os`, `.data.wsl`, `.data.chassis`
+   - Platform detection in regular templates: `.chezmoi.os`, `.wsl`, `.chassis`
+   - Platform detection in partials: `.data.chezmoi.os`, `.data.wsl`, `.data.chassis`
    - Doppler secrets: `{{ dopplerProjectJson.SECRET_NAME }}`
    - Conditional logic: `{{ if }}...{{ else }}...{{ end }}`
+   - Example partial call: `{{ template "commonrc.sh.tmpl" . }}` (passes entire context as `data`)
 
 5. **Suggest TODO list updates** (but DO NOT modify automatically)
    - When a task is completed, check if `TODO.md` exists in the repository

home/dot_claude/CLAUDE.md.tmpl

@@ -1,4 +1,6 @@
- **Note**: Project-specific CLAUDE.md files take precedence for project-specific patterns.
+**Note**: Project-specific CLAUDE.md files take precedence for project-specific patterns.
+
+{{- if and (eq .chezmoi.os "windows") (not .wsl) }}
 
 ## Shell Environment (Windows)
 
@@ -7,6 +9,25 @@
 - ❌ Do NOT use CMD commands (`dir`, `copy`, `del`)
 - ✅ Use standard Bash/Unix commands (`ls`, `cp`, `mv`, `rm`, `grep`)
 - Prefer relative paths for simplicity
+{{- else if .wsl }}
+
+## Shell Environment (WSL)
+
+- **You are in WSL (Windows Subsystem for Linux)**
+- ✅ Use standard Linux/Bash commands (`ls`, `cp`, `mv`, `rm`, `grep`)
+- ✅ Full access to Linux tooling and package managers
+- ⚠️ Can access Windows filesystem via `/mnt/c/`, but prefer Linux paths
+- ⚠️ Can call Windows executables (`.exe`), but prefer native Linux tools
+- Prefer relative paths for simplicity
+{{- else if eq .chezmoi.os "linux" }}
+
+## Shell Environment (Linux)
+
+- **You are in a standard Linux environment**
+- ✅ Use standard Bash/Unix commands (`ls`, `cp`, `mv`, `rm`, `grep`)
+- ✅ Full access to Linux tooling and package managers
+- Prefer relative paths for simplicity
+{{- end }}
 
 ## Build & Package Management