feat(state): add file‑tree and repository‑search state modules

Introduce `FileTreeState` for managing a navigable file hierarchy with Git decorations, filtering, and cursor/scroll handling.
Add `RepoSearchState` and related types to support asynchronous ripgrep‑backed repository searches, including result aggregation, pagination, and UI interaction.

crates/owlen-core/src/state/mod.rs

@@ -21,6 +21,8 @@ pub enum InputMode {
     Command,
     SessionBrowser,
     ThemeBrowser,
+    RepoSearch,
+    SymbolSearch,
 }
 
 impl fmt::Display for InputMode {
@@ -35,6 +37,8 @@ impl fmt::Display for InputMode {
             InputMode::Command => "Command",
             InputMode::SessionBrowser => "Sessions",
             InputMode::ThemeBrowser => "Themes",
+            InputMode::RepoSearch => "Search",
+            InputMode::SymbolSearch => "Symbols",
         };
         f.write_str(label)
     }
@@ -43,6 +47,7 @@ impl fmt::Display for InputMode {
 /// Represents which panel is currently focused in the TUI layout.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum FocusedPanel {
+    Files,
     Chat,
     Thinking,
     Input,