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>

src/domains/router.py

@@ -7,9 +7,9 @@ main.py only includes this root_router.
 from fastapi import APIRouter
 
 from src.domains.health.router import router as health_router
+from src.domains.agents.router import router as agents_router
 
 # from src.domains.auth.router import router as auth_router
-# from src.domains.agents.router import router as agents_router
 # from src.domains.tools.router import router as tools_router
 
 root_router = APIRouter()
@@ -17,11 +17,11 @@ root_router = APIRouter()
 # Health (no prefix - root level)
 root_router.include_router(health_router)
 
+# Agents domain (prefix defined in router)
+root_router.include_router(agents_router)
+
 # Auth domain
 # root_router.include_router(auth_router, prefix="/auth", tags=["Auth"])
 
-# Agents domain
-# root_router.include_router(agents_router, prefix="/agents", tags=["Agents"])
-
 # Tools domain
 # root_router.include_router(tools_router, prefix="/tools", tags=["Tools"])