feat(v2): complete multi-LLM providers, TUI redesign, and advanced agent features

Multi-LLM Provider Support:
- Add llm-core crate with LlmProvider trait abstraction
- Implement Anthropic Claude API client with streaming
- Implement OpenAI API client with streaming
- Add token counting with SimpleTokenCounter and ClaudeTokenCounter
- Add retry logic with exponential backoff and jitter

Borderless TUI Redesign:
- Rewrite theme system with terminal capability detection (Full/Unicode256/Basic)
- Add provider tabs component with keybind switching [1]/[2]/[3]
- Implement vim-modal input (Normal/Insert/Visual/Command modes)
- Redesign chat panel with timestamps and streaming indicators
- Add multi-provider status bar with cost tracking
- Add Nerd Font icons with graceful ASCII fallbacks
- Add syntax highlighting (syntect) and markdown rendering (pulldown-cmark)

Advanced Agent Features:
- Add system prompt builder with configurable components
- Enhance subagent orchestration with parallel execution
- Add git integration module for safe command detection
- Add streaming tool results via channels
- Expand tool set: AskUserQuestion, TodoWrite, LS, MultiEdit, BashOutput, KillShell
- Add WebSearch with provider abstraction

Plugin System Enhancement:
- Add full agent definition parsing from YAML frontmatter
- Add skill system with progressive disclosure
- Wire plugin hooks into HookManager

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

crates/tools/todo/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "tools-todo"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+rust-version.workspace = true
+
+[dependencies]
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+parking_lot = "0.12"
+color-eyre = "0.6"

crates/tools/todo/src/lib.rs

@@ -0,0 +1,113 @@
+//! TodoWrite tool for task list management
+
+use parking_lot::RwLock;
+use serde::{Deserialize, Serialize};
+use std::sync::Arc;
+
+/// Status of a todo item
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum TodoStatus {
+    Pending,
+    InProgress,
+    Completed,
+}
+
+/// A todo item
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Todo {
+    pub content: String,
+    pub status: TodoStatus,
+    pub active_form: String,  // Present continuous form for display
+}
+
+/// Shared todo list state
+#[derive(Debug, Clone, Default)]
+pub struct TodoList {
+    inner: Arc<RwLock<Vec<Todo>>>,
+}
+
+impl TodoList {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Replace all todos with new list
+    pub fn write(&self, todos: Vec<Todo>) {
+        *self.inner.write() = todos;
+    }
+
+    /// Get current todos
+    pub fn read(&self) -> Vec<Todo> {
+        self.inner.read().clone()
+    }
+
+    /// Get the current in-progress task (for status display)
+    pub fn current_task(&self) -> Option<String> {
+        self.inner.read()
+            .iter()
+            .find(|t| t.status == TodoStatus::InProgress)
+            .map(|t| t.active_form.clone())
+    }
+
+    /// Get summary stats
+    pub fn stats(&self) -> (usize, usize, usize) {
+        let todos = self.inner.read();
+        let pending = todos.iter().filter(|t| t.status == TodoStatus::Pending).count();
+        let in_progress = todos.iter().filter(|t| t.status == TodoStatus::InProgress).count();
+        let completed = todos.iter().filter(|t| t.status == TodoStatus::Completed).count();
+        (pending, in_progress, completed)
+    }
+
+    /// Format todos for display
+    pub fn format_display(&self) -> String {
+        let todos = self.inner.read();
+        if todos.is_empty() {
+            return "No tasks".to_string();
+        }
+
+        todos.iter().enumerate().map(|(i, t)| {
+            let status_icon = match t.status {
+                TodoStatus::Pending => "○",
+                TodoStatus::InProgress => "◐",
+                TodoStatus::Completed => "●",
+            };
+            format!("{}. {} {}", i + 1, status_icon, t.content)
+        }).collect::<Vec<_>>().join("\n")
+    }
+}
+
+/// Parse todos from JSON tool input
+pub fn parse_todos(input: &serde_json::Value) -> color_eyre::Result<Vec<Todo>> {
+    let todos = input.get("todos")
+        .ok_or_else(|| color_eyre::eyre::eyre!("Missing 'todos' field"))?;
+
+    serde_json::from_value(todos.clone())
+        .map_err(|e| color_eyre::eyre::eyre!("Invalid todos format: {}", e))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_todo_list() {
+        let list = TodoList::new();
+
+        list.write(vec![
+            Todo {
+                content: "First task".to_string(),
+                status: TodoStatus::Completed,
+                active_form: "Completing first task".to_string(),
+            },
+            Todo {
+                content: "Second task".to_string(),
+                status: TodoStatus::InProgress,
+                active_form: "Working on second task".to_string(),
+            },
+        ]);
+
+        assert_eq!(list.current_task(), Some("Working on second task".to_string()));
+        assert_eq!(list.stats(), (0, 1, 1));
+    }
+}