feat(podcast): add pre-estimate endpoint, enhance cost estimator with multi-model support, cleanup alpha pricing seeding

- Add POST /podcast/pre-estimate endpoint for cost estimation before analysis
- Enhance cost_estimator.py with multi-model support (gemini, audio, voice clone, image, video)
- Add detailed cost breakdown (llm, audio, media costs + per-phase breakdown)
- Remove redundant pricing seeding from init_alpha_subscription_tiers.py
- Add SSOT pricing via PricingService.initialize_default_pricing()
- Update TopicUrlInput tooltip to show estimate details
- Add debug logging for pricing seeding and pre-estimate
- Clean up verbose podcast mode debug logs in app.py

backend/api/podcast/prompts/__init__.py

@@ -0,0 +1,24 @@
+"""
+Prompts module for podcast topic enhancement.
+"""
+
+from .website_enhance_prompts import (
+    get_enhance_topic_prompt,
+    format_website_context,
+    STANDARD_ENHANCE_PROMPT,
+    WEBSITE_AWARE_ENHANCE_PROMPT,
+)
+
+from services.podcast_context_builder import (
+    PodcastContextBuilder,
+    context_builder,
+)
+
+__all__ = [
+    "get_enhance_topic_prompt",
+    "format_website_context",
+    "STANDARD_ENHANCE_PROMPT",
+    "WEBSITE_AWARE_ENHANCE_PROMPT",
+    "PodcastContextBuilder",
+    "context_builder",
+]