Add initial project structure and core functionality for ArchDoc

- Created `.gitignore` files for various directories to exclude unnecessary files.
- Added `PLAN.md` to outline the project goals and architecture documentation generation.
- Implemented the `archdoc-cli` with a command-line interface for initializing and generating documentation.
- Developed the `archdoc-core` library for analyzing Python projects and generating architecture documentation.
- Included caching mechanisms to optimize repeated analysis.
- Established a comprehensive test suite to ensure functionality and error handling.
- Updated `README.md` to provide an overview and installation instructions for ArchDoc.

archdoc-core/src/scanner.rs

@@ -0,0 +1,86 @@
+//! File scanner for ArchDoc
+//!
+//! This module handles scanning the file system for Python files according to
+//! the configuration settings.
+
+use crate::config::Config;
+use crate::errors::ArchDocError;
+use std::path::{Path, PathBuf};
+use walkdir::WalkDir;
+
+pub struct FileScanner {
+    config: Config,
+}
+
+impl FileScanner {
+    pub fn new(config: Config) -> Self {
+        Self { config }
+    }
+    
+    pub fn scan_python_files(&self, root: &Path) -> Result<Vec<PathBuf>, ArchDocError> {
+        // Check if root directory exists
+        if !root.exists() {
+            return Err(ArchDocError::Io(std::io::Error::new(
+                std::io::ErrorKind::NotFound,
+                format!("Root directory does not exist: {}", root.display())
+            )));
+        }
+        
+        if !root.is_dir() {
+            return Err(ArchDocError::Io(std::io::Error::new(
+                std::io::ErrorKind::InvalidInput,
+                format!("Root path is not a directory: {}", root.display())
+            )));
+        }
+        
+        let mut python_files = Vec::new();
+        
+        // Walk directory tree respecting include/exclude patterns
+        for entry in WalkDir::new(root)
+            .follow_links(self.config.scan.follow_symlinks)
+            .into_iter() {
+            
+            let entry = entry.map_err(|e| {
+                ArchDocError::Io(std::io::Error::new(
+                    std::io::ErrorKind::Other,
+                    format!("Failed to read directory entry: {}", e)
+                ))
+            })?;
+            
+            let path = entry.path();
+            
+            // Skip excluded paths
+            if self.is_excluded(path) {
+                if path.is_dir() {
+                    continue;
+                } else {
+                    continue;
+                }
+            }
+            
+            // Include Python files
+            if path.extension().and_then(|s| s.to_str()) == Some("py") {
+                python_files.push(path.to_path_buf());
+            }
+        }
+        
+        Ok(python_files)
+    }
+    
+    fn is_excluded(&self, path: &Path) -> bool {
+        // Convert path to string for pattern matching
+        let path_str = match path.to_str() {
+            Some(s) => s,
+            None => return false, // If we can't convert to string, don't exclude
+        };
+        
+        // Check if path matches any exclude patterns
+        for pattern in &self.config.scan.exclude {
+            if path_str.contains(pattern) {
+                return true;
+            }
+        }
+        
+        false
+    }
+}