refactor: extract constants, parameterize validators, simplify factory

Quick-win refactors from the Refactoring Guru catalog:

- Replace Magic Number with Symbolic Constant: extract DEFAULT_TIMEOUT_MS,
  DEFAULT_MAX_RETRIES, DEFAULT_MAX_TOKENS, DEFAULT_TEMPERATURE, default
  models per provider, and validation prompt into src/constants.ts.
- Parameterize Method: collapse validateTemperature / validateTopP /
  validateMaxTokens (and the inline timeout/maxRetries checks) into a
  single validateNumberInRange helper with bounds metadata.
- Inline Class / Remove Middle Man: drop the unused ProviderRegistry
  class from utils/factory.ts. createProvider now dispatches through
  the PROVIDER_REGISTRY const directly instead of a parallel switch.

Also fixes stale VERSION constant in src/index.ts (was 1.3.1).

src/providers/claude.ts

@@ -34,6 +34,13 @@ import type {
 } from '../types/index.js';
 import { BaseAIProvider } from './base.js';
 import { AIProviderError, AIErrorType } from '../types/index.js';
+import {
+  DEFAULT_ANTHROPIC_VERSION,
+  DEFAULT_MAX_TOKENS,
+  DEFAULT_MODELS,
+  DEFAULT_TEMPERATURE,
+  VALIDATION_PROMPT
+} from '../constants.js';
 
 // ============================================================================
 // TYPES AND INTERFACES
@@ -153,9 +160,8 @@ export class ClaudeProvider extends BaseAIProvider {
   constructor(config: ClaudeConfig) {
     super(config);
     
-    // Set Claude-specific defaults
-    this.defaultModel = config.defaultModel || 'claude-3-5-sonnet-20241022';
-    this.version = config.version || '2023-06-01';
+    this.defaultModel = config.defaultModel || DEFAULT_MODELS.claude;
+    this.version = config.version || DEFAULT_ANTHROPIC_VERSION;
     
     // Validate model name format
     this.validateModelName(this.defaultModel);
@@ -329,11 +335,10 @@ export class ClaudeProvider extends BaseAIProvider {
     }
 
     try {
-      // Make minimal request to test connection and permissions
       await this.client.messages.create({
         model: this.defaultModel,
         max_tokens: 1,
-        messages: [{ role: 'user', content: 'Hi' }]
+        messages: [{ role: 'user', content: VALIDATION_PROMPT }]
       });
       
     } catch (error: any) {
@@ -449,8 +454,8 @@ export class ClaudeProvider extends BaseAIProvider {
   ) {
     return {
       model: params.model || this.defaultModel,
-      max_tokens: params.maxTokens || 1000,
-      temperature: params.temperature ?? 0.7,
+      max_tokens: params.maxTokens || DEFAULT_MAX_TOKENS,
+      temperature: params.temperature ?? DEFAULT_TEMPERATURE,
       top_p: params.topP,
       stop_sequences: params.stopSequences,
       system: system || undefined,