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/app/ui/src/components/provider_tabs.rs

@@ -0,0 +1,189 @@
+//! Provider tabs component for multi-LLM support
+//!
+//! Displays horizontal tabs for switching between providers (Claude, Ollama, OpenAI)
+//! with icons and keybind hints.
+
+use crate::theme::{Provider, Theme};
+use ratatui::{
+    layout::Rect,
+    style::Style,
+    text::{Line, Span},
+    widgets::Paragraph,
+    Frame,
+};
+
+/// Provider tab state and rendering
+pub struct ProviderTabs {
+    active: Provider,
+    theme: Theme,
+}
+
+impl ProviderTabs {
+    /// Create new provider tabs with default provider
+    pub fn new(theme: Theme) -> Self {
+        Self {
+            active: Provider::Ollama, // Default to Ollama (local)
+            theme,
+        }
+    }
+
+    /// Create with specific active provider
+    pub fn with_provider(provider: Provider, theme: Theme) -> Self {
+        Self {
+            active: provider,
+            theme,
+        }
+    }
+
+    /// Get the currently active provider
+    pub fn active(&self) -> Provider {
+        self.active
+    }
+
+    /// Set the active provider
+    pub fn set_active(&mut self, provider: Provider) {
+        self.active = provider;
+    }
+
+    /// Cycle to the next provider
+    pub fn next(&mut self) {
+        self.active = match self.active {
+            Provider::Claude => Provider::Ollama,
+            Provider::Ollama => Provider::OpenAI,
+            Provider::OpenAI => Provider::Claude,
+        };
+    }
+
+    /// Cycle to the previous provider
+    pub fn previous(&mut self) {
+        self.active = match self.active {
+            Provider::Claude => Provider::OpenAI,
+            Provider::Ollama => Provider::Claude,
+            Provider::OpenAI => Provider::Ollama,
+        };
+    }
+
+    /// Select provider by number (1, 2, 3)
+    pub fn select_by_number(&mut self, num: u8) {
+        self.active = match num {
+            1 => Provider::Claude,
+            2 => Provider::Ollama,
+            3 => Provider::OpenAI,
+            _ => self.active,
+        };
+    }
+
+    /// Update the theme
+    pub fn set_theme(&mut self, theme: Theme) {
+        self.theme = theme;
+    }
+
+    /// Render the provider tabs (borderless)
+    pub fn render(&self, frame: &mut Frame, area: Rect) {
+        let mut spans = Vec::new();
+
+        // Add spacing at start
+        spans.push(Span::raw("  "));
+
+        for (i, provider) in Provider::all().iter().enumerate() {
+            let is_active = *provider == self.active;
+            let icon = self.theme.provider_icon(*provider);
+            let name = provider.name();
+            let number = (i + 1).to_string();
+
+            // Keybind hint
+            spans.push(Span::styled(
+                format!("[{}] ", number),
+                self.theme.status_dim,
+            ));
+
+            // Icon and name
+            let style = if is_active {
+                Style::default()
+                    .fg(self.theme.provider_color(*provider))
+                    .add_modifier(ratatui::style::Modifier::BOLD)
+            } else {
+                self.theme.tab_inactive
+            };
+
+            spans.push(Span::styled(format!("{} ", icon), style));
+            spans.push(Span::styled(name.to_string(), style));
+
+            // Separator between tabs (not after last)
+            if i < Provider::all().len() - 1 {
+                spans.push(Span::styled(
+                    format!("  {}  ", self.theme.symbols.vertical_separator),
+                    self.theme.status_dim,
+                ));
+            }
+        }
+
+        // Tab cycling hint on the right
+        spans.push(Span::raw("  "));
+        spans.push(Span::styled("[Tab] cycle", self.theme.status_dim));
+
+        let line = Line::from(spans);
+        let paragraph = Paragraph::new(line);
+        frame.render_widget(paragraph, area);
+    }
+
+    /// Render a compact version (just active provider)
+    pub fn render_compact(&self, frame: &mut Frame, area: Rect) {
+        let icon = self.theme.provider_icon(self.active);
+        let name = self.active.name();
+
+        let line = Line::from(vec![
+            Span::raw("  "),
+            Span::styled(
+                format!("{} {}", icon, name),
+                Style::default()
+                    .fg(self.theme.provider_color(self.active))
+                    .add_modifier(ratatui::style::Modifier::BOLD),
+            ),
+        ]);
+
+        let paragraph = Paragraph::new(line);
+        frame.render_widget(paragraph, area);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_provider_cycling() {
+        let theme = Theme::default();
+        let mut tabs = ProviderTabs::new(theme);
+
+        assert_eq!(tabs.active(), Provider::Ollama);
+
+        tabs.next();
+        assert_eq!(tabs.active(), Provider::OpenAI);
+
+        tabs.next();
+        assert_eq!(tabs.active(), Provider::Claude);
+
+        tabs.next();
+        assert_eq!(tabs.active(), Provider::Ollama);
+    }
+
+    #[test]
+    fn test_select_by_number() {
+        let theme = Theme::default();
+        let mut tabs = ProviderTabs::new(theme);
+
+        tabs.select_by_number(1);
+        assert_eq!(tabs.active(), Provider::Claude);
+
+        tabs.select_by_number(2);
+        assert_eq!(tabs.active(), Provider::Ollama);
+
+        tabs.select_by_number(3);
+        assert_eq!(tabs.active(), Provider::OpenAI);
+
+        // Invalid number should not change
+        tabs.select_by_number(4);
+        assert_eq!(tabs.active(), Provider::OpenAI);
+    }
+}