Add go-llm v2: redesigned API for simpler LLM abstraction

v2 is a new Go module (v2/) with a dramatically simpler API:
- Unified Message type (no more Input marker interface)
- Define[T] for ergonomic tool creation with standard context.Context
- Chat session with automatic tool-call loop (agent loop)
- Streaming via pull-based StreamReader
- MCP one-call connect (MCPStdioServer, MCPHTTPServer, MCPSSEServer)
- Middleware support (logging, retry, timeout, usage tracking)
- Decoupled JSON Schema (map[string]any, no provider coupling)
- Sample tools: WebSearch, Browser, Exec, ReadFile, WriteFile, HTTP
- Providers: OpenAI, Anthropic, Google (all with streaming)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

v2/tools/writefile.go

@@ -0,0 +1,31 @@
+package tools
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	llm "gitea.stevedudenhoeffer.com/steve/go-llm/v2"
+)
+
+// WriteFileParams defines parameters for the write file tool.
+type WriteFileParams struct {
+	Path    string `json:"path" description:"File path to write"`
+	Content string `json:"content" description:"Content to write to the file"`
+}
+
+// WriteFile creates a file writing tool.
+//
+// Example:
+//
+//	tools := llm.NewToolBox(tools.WriteFile())
+func WriteFile() llm.Tool {
+	return llm.Define[WriteFileParams]("write_file", "Write content to a file (creates or overwrites)",
+		func(ctx context.Context, p WriteFileParams) (string, error) {
+			if err := os.WriteFile(p.Path, []byte(p.Content), 0644); err != nil {
+				return "", fmt.Errorf("writing file: %w", err)
+			}
+			return fmt.Sprintf("Successfully wrote %d bytes to %s", len(p.Content), p.Path), nil
+		},
+	)
+}