feat: add native Gemini provider for Google AI models

Adds Google Gemini as a first-class provider using Gemini's OpenAI-compatible
endpoint, supporting gemini-2.0-flash, gemini-2.5-pro, and gemini-2.0-flash-lite
across all three model tiers (opus/sonnet/haiku).

- Add 'gemini' to APIProvider type with CLAUDE_CODE_USE_GEMINI env detection
- Map all 11 model configs to appropriate Gemini models per tier
- Route Gemini through existing OpenAI shim (generativelanguage.googleapis.com)
- Support GEMINI_API_KEY and GOOGLE_API_KEY for authentication
- Fix model display name to show actual Gemini model instead of Claude fallback
- Add Gemini support to provider-launch, provider-bootstrap, system-check scripts
- Add dev:gemini npm script for local development

Bootstrap: bun run profile:init -- --provider gemini --api-key <key>
Launch: bun run dev:gemini

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

src/utils/model/providers.ts

@@ -1,18 +1,20 @@
 import type { AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS } from '../../services/analytics/index.js'
 import { isEnvTruthy } from '../envUtils.js'
 
-export type APIProvider = 'firstParty' | 'bedrock' | 'vertex' | 'foundry' | 'openai'
+export type APIProvider = 'firstParty' | 'bedrock' | 'vertex' | 'foundry' | 'openai' | 'gemini'
 
 export function getAPIProvider(): APIProvider {
-  return isEnvTruthy(process.env.CLAUDE_CODE_USE_OPENAI)
-    ? 'openai'
-    : isEnvTruthy(process.env.CLAUDE_CODE_USE_BEDROCK)
-      ? 'bedrock'
-      : isEnvTruthy(process.env.CLAUDE_CODE_USE_VERTEX)
-        ? 'vertex'
-        : isEnvTruthy(process.env.CLAUDE_CODE_USE_FOUNDRY)
-          ? 'foundry'
-          : 'firstParty'
+  return isEnvTruthy(process.env.CLAUDE_CODE_USE_GEMINI)
+    ? 'gemini'
+    : isEnvTruthy(process.env.CLAUDE_CODE_USE_OPENAI)
+      ? 'openai'
+      : isEnvTruthy(process.env.CLAUDE_CODE_USE_BEDROCK)
+        ? 'bedrock'
+        : isEnvTruthy(process.env.CLAUDE_CODE_USE_VERTEX)
+          ? 'vertex'
+          : isEnvTruthy(process.env.CLAUDE_CODE_USE_FOUNDRY)
+            ? 'foundry'
+            : 'firstParty'
 }
 
 export function getAPIProviderForStatsig(): AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS {