feat: add Explore agent with PydanticAI tool calling

Implements the first Claude-like agent for codebase exploration:

Core Features:
- Explore agent with glob, grep, read, and bash tools
- Native PydanticAI tool calling with Ollama/Mistral Nemo
- Sanitized Ollama provider (fixes content:null issue)
- REST API endpoints for agent execution

Tool Infrastructure:
- BaseTool abstract class with ToolResult dataclass
- ReadFileTool, GlobFilesTool, GrepContentTool, BashReadOnlyTool
- Path validation and sandboxing support

CLI Client (separate package for future extraction):
- webber-cli command with chat, explore, status commands
- Communicates with Webber API backend
- Rich console output with theming

Configuration:
- Dev server on port 8095 (production uses 8086)
- Mistral Nemo optimizations (temp 0.3, tool_choice required)

Tests: 24 tests covering tools and API endpoints

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cli/theme.py

@@ -0,0 +1,75 @@
+"""
+CLI theme configuration.
+
+Centralized color and style definitions.
+"""
+from dataclasses import dataclass
+from functools import lru_cache
+
+from rich.console import Console
+from rich.theme import Theme
+
+
+@dataclass(frozen=True)
+class ThemeColors:
+    """Color palette for the CLI."""
+
+    # Semantic colors
+    info: str = "steel_blue"
+    warning: str = "dark_orange"
+    error: str = "red3"
+    success: str = "sea_green3"
+
+    # UI elements
+    prompt: str = "steel_blue bold"
+    title: str = "steel_blue bold"
+    path: str = "steel_blue underline"
+    code: str = "sea_green3"
+    highlight: str = "medium_purple1"
+    dim: str = "dim white"
+
+    # Panel borders
+    border_default: str = "steel_blue"
+    border_success: str = "sea_green3"
+    border_error: str = "red3"
+    border_warning: str = "dark_orange"
+
+
+@dataclass(frozen=True)
+class ThemeConfig:
+    """Complete theme configuration."""
+
+    colors: ThemeColors = ThemeColors()
+    spinner: str = "dots"
+    syntax_theme: str = "monokai"
+
+    def to_rich_theme_dict(self) -> dict[str, str]:
+        """Convert to Rich theme dictionary."""
+        return {
+            "info": self.colors.info,
+            "warning": self.colors.warning,
+            "error": self.colors.error,
+            "success": self.colors.success,
+            "prompt": self.colors.prompt,
+            "title": self.colors.title,
+            "path": self.colors.path,
+            "code": self.colors.code,
+            "highlight": self.colors.highlight,
+            "dim": self.colors.dim,
+        }
+
+
+DEFAULT_THEME = ThemeConfig()
+
+
+def get_theme() -> ThemeConfig:
+    """Get the current theme configuration."""
+    return DEFAULT_THEME
+
+
+@lru_cache
+def get_console() -> Console:
+    """Get the shared console instance with theme applied."""
+    theme = get_theme()
+    rich_theme = Theme(theme.to_rich_theme_dict())
+    return Console(theme=rich_theme)