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/services/api/openaiShim.ts

@@ -741,6 +741,22 @@ export function createOpenAIShimClient(options: {
   maxRetries?: number
   timeout?: number
 }): unknown {
+  // When Gemini provider is active, map Gemini env vars to OpenAI-compatible ones
+  // so the existing providerConfig.ts infrastructure picks them up correctly.
+  if (
+    process.env.CLAUDE_CODE_USE_GEMINI === '1' ||
+    process.env.CLAUDE_CODE_USE_GEMINI === 'true'
+  ) {
+    process.env.OPENAI_BASE_URL ??=
+      process.env.GEMINI_BASE_URL ??
+      'https://generativelanguage.googleapis.com/v1beta/openai'
+    process.env.OPENAI_API_KEY ??=
+      process.env.GEMINI_API_KEY ?? process.env.GOOGLE_API_KEY ?? ''
+    if (process.env.GEMINI_MODEL && !process.env.OPENAI_MODEL) {
+      process.env.OPENAI_MODEL = process.env.GEMINI_MODEL
+    }
+  }
+
   const beta = new OpenAIShimBeta({
     ...(options.defaultHeaders ?? {}),
   })