Devon own stem/track/channel, per-category LLM routing, settings UI cleanup

Audio:
- Devon gets own stem, Reaper track (Input 17), and configurable channel
- play_caller_audio accepts stem_name + channel_override params
- Reaper script checks 4 voice tracks (Host, Devon, Live Caller, AI Caller)
- postprod.py includes devon stem in gap detection

Cost optimization:
- Per-category model routing: Sonnet for caller dialog, Gemini Flash for everything else
- Estimated 65% cost reduction ($4.32 → ~$1.50/show)
- Category models configurable from settings UI

Frontend:
- Settings panel: clean routing grid for output channels, model routing grid for LLM categories
- Devon channel added to audio routing
- Share icon SVG fill fix (currentColor)
- Website homepage iterations

Publishing:
- Revert Castopod API workaround (API re-enabled)
- Fix container media path

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/services/intern.py

@@ -15,7 +15,7 @@ from .news import news_service, SEARXNG_URL
 DATA_FILE = Path(__file__).parent.parent.parent / "data" / "intern.json"
 
 # Model for intern — good at tool use, same as primary
-INTERN_MODEL = "anthropic/claude-sonnet-4-5"
+INTERN_MODEL = None  # uses category-based routing from config
 
 INTERN_SYSTEM_PROMPT = """You are Devon, the 23-year-old intern on "Luke at the Roost," a late-night radio show. You are NOT Luke. Luke is the HOST — he talks to callers, runs the show, and is your boss. You work behind the scenes and occasionally get pulled into conversations.