docs: add CLI doctor error code documentation

docs/error-codes.md

@@ -0,0 +1,122 @@
+# Facetpack CLI Doctor – Error Codes
+
+This document explains the error codes generated by the Facetpack CLI Doctor.
+Each error code helps identify a specific syntax or usage issue and provides
+guidance on how to resolve it.
+
+---
+
+## E0000 – Unknown parsing error
+
+**Description:**  
+An unspecified parsing error occurred.
+
+**Common causes:**
+- Unsupported or malformed syntax
+- Incomplete or corrupted source file
+
+**How to fix:**
+- Review the reported line and surrounding code
+- Ensure the file contains valid JavaScript/TypeScript syntax
+
+---
+
+## E0001 – Expected token not found
+
+**Description:**  
+The parser expected a specific token but encountered a different one.
+
+**Common causes:**
+- Missing closing braces `}`, parentheses `)`, or brackets `]`
+- Missing semicolons or punctuation
+
+**How to fix:**
+- Check for unclosed blocks or expressions
+- Ensure all syntax elements are properly closed
+
+---
+
+## E0002 – Unexpected token
+
+**Description:**  
+An unexpected token was encountered during parsing.
+
+**Common causes:**
+- Typographical errors
+- Invalid syntax for the current context
+
+**How to fix:**
+- Verify the syntax near the reported location
+- Remove or correct the unexpected token
+
+---
+
+## E0003 – Unterminated construct
+
+**Description:**  
+A string, comment, or other construct was not properly terminated.
+
+**Common causes:**
+- Missing closing quotes (`'`, `"`, `` ` ``)
+- Unclosed block comments
+
+**How to fix:**
+- Ensure all strings and comments are properly closed
+
+---
+
+## E0004 – Reserved word usage
+
+**Description:**  
+A reserved keyword was used incorrectly.
+
+**Common causes:**
+- Using JavaScript reserved words as variable or function names
+
+**How to fix:**
+- Rename the identifier to a non-reserved word
+
+---
+
+## E0005 – Invalid `return` usage
+
+**Description:**  
+The `return` keyword was used in an invalid context.
+
+**Common causes:**
+- Using `return` outside of a function body
+
+**How to fix:**
+- Ensure `return` statements are only used inside functions
+
+---
+
+## E0006 – Invalid `await` usage
+
+**Description:**  
+The `await` keyword was used where it is not allowed.
+
+**Common causes:**
+- Using `await` outside of an `async` function
+
+**How to fix:**
+- Wrap the code in an `async` function or remove `await`
+
+---
+
+## E0007 – Invalid `import` or `export` usage
+
+**Description:**  
+The `import` or `export` statement was used incorrectly.
+
+**Common causes:**
+- Using `import`/`export` in non-module files
+- Incorrect module syntax
+
+**How to fix:**
+- Ensure the file is treated as a module
+- Verify correct usage of `import` and `export` statements
+
+
+
+