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/ask/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "tools-ask"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+tokio = { version = "1", features = ["sync"] }
+color-eyre = "0.6"

crates/tools/ask/src/lib.rs

@@ -0,0 +1,60 @@
+//! AskUserQuestion tool for interactive user input
+
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+use tokio::sync::{mpsc, oneshot};
+
+/// A question option
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct QuestionOption {
+    pub label: String,
+    pub description: String,
+}
+
+/// A question to ask the user
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Question {
+    pub question: String,
+    pub header: String,
+    pub options: Vec<QuestionOption>,
+    pub multi_select: bool,
+}
+
+/// Request sent to the UI to ask questions
+#[derive(Debug)]
+pub struct AskRequest {
+    pub questions: Vec<Question>,
+    pub response_tx: oneshot::Sender<HashMap<String, String>>,
+}
+
+/// Channel for sending ask requests to the UI
+pub type AskSender = mpsc::Sender<AskRequest>;
+pub type AskReceiver = mpsc::Receiver<AskRequest>;
+
+/// Create a channel pair for ask requests
+pub fn create_ask_channel() -> (AskSender, AskReceiver) {
+    mpsc::channel(1)
+}
+
+/// Ask the user questions (called by agent)
+pub async fn ask_user(
+    sender: &AskSender,
+    questions: Vec<Question>,
+) -> color_eyre::Result<HashMap<String, String>> {
+    let (response_tx, response_rx) = oneshot::channel();
+
+    sender.send(AskRequest { questions, response_tx }).await
+        .map_err(|_| color_eyre::eyre::eyre!("Failed to send ask request"))?;
+
+    response_rx.await
+        .map_err(|_| color_eyre::eyre::eyre!("Failed to receive ask response"))
+}
+
+/// Parse questions from JSON tool input
+pub fn parse_questions(input: &serde_json::Value) -> color_eyre::Result<Vec<Question>> {
+    let questions = input.get("questions")
+        .ok_or_else(|| color_eyre::eyre::eyre!("Missing 'questions' field"))?;
+
+    serde_json::from_value(questions.clone())
+        .map_err(|e| color_eyre::eyre::eyre!("Invalid questions format: {}", e))
+}