refactor: restructure project directories for better modularity

- Delete llm/ dead code (3 files, zero references)
- Split mcp/ into sub-packages: mcp/provider/ (8 providers) and
  mcp/payment/ (4 payment clients) with registry pattern
- Export Client internal fields and ClientHooks interface for
  sub-package access
- Split api/server.go (3892 lines) into 8 domain-specific handler files
- Split trader/auto_trader.go (2296 lines) into 5 focused files
- Reorganize web/src/components/ flat files into auth/, charts/,
  trader/, common/, modals/, backtest/ subdirectories
- Update all consumer imports to use registry-based provider creation

mcp/interface.go

@@ -1,10 +1,15 @@
 package mcp
 
 import (
-	"net/http"
 	"time"
 )
 
+// ClientEmbedder is implemented by provider types that embed *Client,
+// allowing generic extraction of the underlying base client (e.g. for cloning).
+type ClientEmbedder interface {
+	BaseClient() *Client
+}
+
 // AIClient public AI client interface (for external use)
 type AIClient interface {
 	SetAPIKey(apiKey string, customURL string, customModel string)
@@ -21,41 +26,3 @@ type AIClient interface {
 	// (LLMResponse.ToolCalls), but not both.
 	CallWithRequestFull(req *Request) (*LLMResponse, error)
 }
-
-// clientHooks is the internal dispatch interface used to implement per-provider
-// polymorphism without Go's lack of virtual methods.
-//
-// Each method can be overridden by an embedding struct (e.g. ClaudeClient).
-// The base *Client provides OpenAI-compatible defaults; providers with a
-// different wire format (Anthropic, Gemini native, etc.) override only what
-// differs.  All call-path methods in client.go invoke these via c.hooks so
-// that the override is always picked up at runtime.
-type clientHooks interface {
-	// ── Simple CallWithMessages path ────────────────────────────────────────
-	call(systemPrompt, userPrompt string) (string, error)
-	buildMCPRequestBody(systemPrompt, userPrompt string) map[string]any
-
-	// ── Shared request plumbing ─────────────────────────────────────────────
-	buildUrl() string
-	buildRequest(url string, jsonData []byte) (*http.Request, error)
-	setAuthHeader(reqHeaders http.Header)
-	marshalRequestBody(requestBody map[string]any) ([]byte, error)
-
-	// ── Advanced (Request-object) path ──────────────────────────────────────
-	// buildRequestBodyFromRequest converts a *Request into the provider's
-	// native wire-format map.  Providers that use a different protocol (e.g.
-	// Anthropic uses "input_schema" for tools, "tool_use" content blocks, and
-	// a top-level "system" field) override this method.
-	buildRequestBodyFromRequest(req *Request) map[string]any
-
-	// parseMCPResponse extracts the plain-text reply from a non-streaming
-	// response body.
-	parseMCPResponse(body []byte) (string, error)
-
-	// parseMCPResponseFull extracts both text and tool calls.  Providers whose
-	// response envelope differs from the OpenAI choices[] structure (e.g.
-	// Anthropic content[] with tool_use blocks) override this method.
-	parseMCPResponseFull(body []byte) (*LLMResponse, error)
-
-	isRetryableError(err error) bool
-}