Implement Phase 1: Foundation and cache system

- Add Cargo project with TUI and async dependencies
- Implement cache-only architecture for low bandwidth operation
- Add file scanner with media type detection
- Create two-panel TUI layout (file tree and status)
- Add config file support for scan path management
- Implement XDG-compliant cache and config directories
- Add Gitea CI/CD workflow for automated releases

src/state/mod.rs

@@ -0,0 +1,92 @@
+use crate::cache::{Cache, FileTreeNode};
+use crate::config::Config;
+use std::path::PathBuf;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum PlayerState {
+    Stopped,
+    Playing,
+    Paused,
+}
+
+pub struct AppState {
+    pub cache: Cache,
+    pub config: Config,
+    pub selected_index: usize,
+    pub scroll_offset: usize,
+    pub player_state: PlayerState,
+    pub current_file: Option<PathBuf>,
+    pub current_position: f64,
+    pub current_duration: f64,
+    pub volume: i64,
+    pub should_quit: bool,
+    pub flattened_items: Vec<FlattenedItem>,
+}
+
+#[derive(Debug, Clone)]
+pub struct FlattenedItem {
+    pub node: FileTreeNode,
+    pub depth: usize,
+    pub is_expanded: bool,
+}
+
+impl AppState {
+    pub fn new(cache: Cache, config: Config) -> Self {
+        let flattened_items = flatten_tree(&cache.file_tree, 0);
+
+        Self {
+            cache,
+            config,
+            selected_index: 0,
+            scroll_offset: 0,
+            player_state: PlayerState::Stopped,
+            current_file: None,
+            current_position: 0.0,
+            current_duration: 0.0,
+            volume: 100,
+            should_quit: false,
+            flattened_items,
+        }
+    }
+
+    pub fn move_selection_up(&mut self) {
+        if self.selected_index > 0 {
+            self.selected_index -= 1;
+        }
+    }
+
+    pub fn move_selection_down(&mut self) {
+        if self.selected_index < self.flattened_items.len().saturating_sub(1) {
+            self.selected_index += 1;
+        }
+    }
+
+    pub fn get_selected_item(&self) -> Option<&FlattenedItem> {
+        self.flattened_items.get(self.selected_index)
+    }
+
+    pub fn refresh_flattened_items(&mut self) {
+        self.flattened_items = flatten_tree(&self.cache.file_tree, 0);
+        if self.selected_index >= self.flattened_items.len() {
+            self.selected_index = self.flattened_items.len().saturating_sub(1);
+        }
+    }
+}
+
+fn flatten_tree(nodes: &[FileTreeNode], depth: usize) -> Vec<FlattenedItem> {
+    let mut result = Vec::new();
+
+    for node in nodes {
+        result.push(FlattenedItem {
+            node: node.clone(),
+            depth,
+            is_expanded: true, // For now, all directories are expanded
+        });
+
+        if node.is_dir && !node.children.is_empty() {
+            result.extend(flatten_tree(&node.children, depth + 1));
+        }
+    }
+
+    result
+}