Address PR review feedback: auth/errors, lazy-load, revert unrelated docs

- get_sub_replies(): add auth check before request, map 402→ChatPaymentRequired
  and 403→ChatAccessDenied to match get_threads()/get_messages() behavior
- ChatThread.author/created_at/comment_count: fetch lazily on first access
  when _thread_data is None, consistent with body property
- get_thread() docstring: accurately describes lazy-fetch behavior for all properties
- Revert unrelated README changes: restore uv install example and CLI section
- Revert unrelated mkdocs.yml change: restore CLI: cli.md nav entry

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: amckenna

README.md

@@ -19,11 +19,38 @@ This library provides Python interfaces for interacting with Substack's unoffici
 # Using pip
 pip install substack-api
 
-# Using poetry
-poetry add substack-api
+# Using uv
+uv add substack-api
 ```
 
-## Usage Examples
+## Command-Line Interface
+
+The library includes a CLI for quick access from the terminal. All commands output JSON by default.
+
+```bash
+# Get the 5 newest posts from a newsletter
+substack newsletter posts https://example.substack.com --limit 5
+
+# Search for posts
+substack newsletter search https://example.substack.com "machine learning"
+
+# Get metadata for a specific post
+substack post metadata https://example.substack.com/p/my-post --pretty
+
+# Look up a user's subscriptions
+substack user subscriptions username
+
+# Browse categories
+substack categories
+substack category newsletters --name Technology
+
+# Run the quickstart guide for a full command reference
+substack quickstart
+```
+
+Use `--pretty` for human-readable output and `--cookies <path>` for authenticated access to paywalled content.
+
+## Python Usage Examples
 
 ### Working with Newsletters
 

mkdocs.yml

@@ -52,6 +52,7 @@ plugins:
 nav:
   - Home: index.md
   - Installation: installation.md
+  - CLI: cli.md
   - User Guide: user-guide.md
   - Authentication: authentication.md
   - API Reference:

substack_api/chat.py

@@ -329,20 +329,29 @@ def author(self) -> Dict[str, Any]:
 
         Contains keys like 'id', 'name', 'handle', 'photo_url'.
         """
+        if self._thread_data:
+            return self._thread_data.get("user", {})
+        self._fetch_thread_data()
         if self._thread_data:
             return self._thread_data.get("user", {})
         return {}
 
     @property
     def created_at(self) -> str:
         """The ISO timestamp when the thread was created."""
+        if self._thread_data:
+            return self._thread_data.get("communityPost", {}).get("created_at", "")
+        self._fetch_thread_data()
         if self._thread_data:
             return self._thread_data.get("communityPost", {}).get("created_at", "")
         return ""
 
     @property
     def comment_count(self) -> int:
         """The number of replies/comments in this thread."""
+        if self._thread_data:
+            return self._thread_data.get("communityPost", {}).get("comment_count", 0)
+        self._fetch_thread_data()
         if self._thread_data:
             return self._thread_data.get("communityPost", {}).get("comment_count", 0)
         return 0
@@ -409,6 +418,11 @@ def get_sub_replies(
         ThreadNotFound
             If the parent reply is not found.
         """
+        if not self.auth or not self.auth.authenticated:
+            raise ChatAuthenticationRequired(
+                "Authentication is required to access sub-replies."
+            )
+
         parent_id = message.id if isinstance(message, ChatMessage) else message
         url = f"{BASE_URL}/community/comments/{parent_id}/comments"
         params = {"order": "asc", "initial": "true"}
@@ -419,6 +433,14 @@ def get_sub_replies(
             raise ChatAuthenticationRequired(
                 "Authentication is required to access sub-replies."
             )
+        elif response.status_code == 402:
+            raise ChatPaymentRequired(
+                "Access to this chat requires a paid subscription or a higher subscription tier."
+            )
+        elif response.status_code == 403:
+            raise ChatAccessDenied(
+                "You do not have permission to access this thread."
+            )
         elif response.status_code == 404:
             raise ThreadNotFound(
                 f"Parent reply with ID '{parent_id}' was not found."
@@ -623,8 +645,9 @@ def get_thread(self, thread_id: str) -> ChatThread:
 
         Notes
         -----
-        This creates a ChatThread object without pre-fetched data.
-        The thread data will be fetched when properties are accessed.
+        This creates a ChatThread without pre-fetched data. All properties
+        (``body``, ``author``, ``created_at``, ``comment_count``) fetch from
+        the API on first access and cache the result.
         """
         return ChatThread(
             publication_id=self._publication_id,