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>

chat.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+# Start webber chat session
+# Usage: ./chat.sh [directory]
+
+DIR="${1:-.}"
+
+cd /mnt/media/Projects/webber
+source .venv/bin/activate
+
+echo "Starting Webber chat..."
+echo "Working directory: $(realpath "$DIR")"
+echo ""
+
+webber chat -d "$DIR"