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/platform/config/src/lib.rs

@@ -5,26 +5,52 @@ use figment::{
 };
 use serde::{Deserialize, Serialize};
 use std::path::PathBuf;
+use std::env;
 use permissions::{Mode, PermissionManager};
+use llm_core::ProviderType;
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Settings {
-    #[serde(default = "default_ollama_url")]
-    pub ollama_url: String,
+    // Provider configuration
+    #[serde(default = "default_provider")]
+    pub provider: String, // "ollama" | "anthropic" | "openai"
+
     #[serde(default = "default_model")]
     pub model: String,
-    #[serde(default = "default_mode")]
-    pub mode: String, // "plan" (read-only) for now
+
+    // Ollama-specific
+    #[serde(default = "default_ollama_url")]
+    pub ollama_url: String,
+
+    // API keys for different providers
     #[serde(default)]
-    pub api_key: Option<String>, // For Ollama Cloud or other API authentication
+    pub api_key: Option<String>, // For Ollama Cloud or backwards compatibility
+
+    #[serde(default)]
+    pub anthropic_api_key: Option<String>,
+
+    #[serde(default)]
+    pub openai_api_key: Option<String>,
+
+    // Permission mode
+    #[serde(default = "default_mode")]
+    pub mode: String, // "plan" | "acceptEdits" | "code"
+}
+
+fn default_provider() -> String {
+    "ollama".into()
 }
 
 fn default_ollama_url() -> String {
     "http://localhost:11434".into()
 }
+
 fn default_model() -> String {
+    // Default model depends on provider, but we use ollama's default here
+    // Users can override this per-provider or use get_effective_model()
     "qwen3:8b".into()
 }
+
 fn default_mode() -> String {
     "plan".into()
 }
@@ -32,10 +58,13 @@ fn default_mode() -> String {
 impl Default for Settings {
     fn default() -> Self {
         Self {
-            ollama_url: default_ollama_url(),
+            provider: default_provider(),
             model: default_model(),
-            mode: default_mode(),
+            ollama_url: default_ollama_url(),
             api_key: None,
+            anthropic_api_key: None,
+            openai_api_key: None,
+            mode: default_mode(),
         }
     }
 }
@@ -51,6 +80,34 @@ impl Settings {
     pub fn get_mode(&self) -> Mode {
         Mode::from_str(&self.mode).unwrap_or(Mode::Plan)
     }
+
+    /// Get the ProviderType enum from the provider string
+    pub fn get_provider(&self) -> Option<ProviderType> {
+        ProviderType::from_str(&self.provider)
+    }
+
+    /// Get the effective model for the current provider
+    /// If no model is explicitly set, returns the provider's default
+    pub fn get_effective_model(&self) -> String {
+        // If model is explicitly set and not the default, use it
+        if self.model != default_model() {
+            return self.model.clone();
+        }
+
+        // Otherwise, use provider-specific default
+        self.get_provider()
+            .map(|p| p.default_model().to_string())
+            .unwrap_or_else(|| self.model.clone())
+    }
+
+    /// Get the API key for the current provider
+    pub fn get_provider_api_key(&self) -> Option<String> {
+        match self.get_provider()? {
+            ProviderType::Ollama => self.api_key.clone(),
+            ProviderType::Anthropic => self.anthropic_api_key.clone(),
+            ProviderType::OpenAI => self.openai_api_key.clone(),
+        }
+    }
 }
 
 pub fn load_settings(project_root: Option<&str>) -> Result<Settings, figment::Error> {
@@ -68,9 +125,31 @@ pub fn load_settings(project_root: Option<&str>) -> Result<Settings, figment::Er
     }
 
     // Environment variables have highest precedence
+    // OWLEN_* prefix (e.g., OWLEN_PROVIDER, OWLEN_MODEL, OWLEN_API_KEY, OWLEN_ANTHROPIC_API_KEY)
     fig = fig.merge(Env::prefixed("OWLEN_").split("__"));
-    // Support OLLAMA_API_KEY, OLLAMA_MODEL, etc. (without nesting)
+
+    // Support OLLAMA_* prefix for backwards compatibility
     fig = fig.merge(Env::prefixed("OLLAMA_"));
 
-    fig.extract()
+    // Support PROVIDER env var (without OWLEN_ prefix)
+    fig = fig.merge(Env::raw().only(&["PROVIDER"]));
+
+    // Extract the settings
+    let mut settings: Settings = fig.extract()?;
+
+    // Manually handle standard provider API key env vars (ANTHROPIC_API_KEY, OPENAI_API_KEY)
+    // These override config files but are overridden by OWLEN_* vars
+    if settings.anthropic_api_key.is_none() {
+        if let Ok(key) = env::var("ANTHROPIC_API_KEY") {
+            settings.anthropic_api_key = Some(key);
+        }
+    }
+
+    if settings.openai_api_key.is_none() {
+        if let Ok(key) = env::var("OPENAI_API_KEY") {
+            settings.openai_api_key = Some(key);
+        }
+    }
+
+    Ok(settings)
 }