refactor(meet-kevin): switch LLM analyzer to OpenRouter via OpenAI SDK

User's Vault has openrouter_api_key but no direct sk-ant-* Anthropic key.
OpenRouter passes through Claude Sonnet 4.6 (~3% markup over Anthropic
list pricing) and matches the existing gpt_mini_endpoint pattern used
by recruiter-responder.

- Replace anthropic.AsyncAnthropic with openai.AsyncOpenAI + base_url
- Convert Anthropic tool-use API to OpenAI function-calling
- System prompt unchanged (analyst instructions are model-agnostic)
- Drop cache_control (not in OpenAI API); revisit later if cost matters
- Model slug: anthropic/claude-sonnet-4.5 (OpenRouter's current Claude tier)
- Pricing: $3.10/M input, $15.50/M output (OpenRouter pass-through)
- Config field anthropic_api_key -> openrouter_api_key
- pyproject extras: anthropic>=0.40 -> openai>=1.50

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

services/meet_kevin_watcher/main.py

@@ -16,7 +16,7 @@ from datetime import timezone
 from decimal import Decimal
 
 import httpx
-from anthropic import AsyncAnthropic
+from openai import AsyncOpenAI
 from sqlalchemy import select
 from sqlalchemy.dialects.postgresql import insert as pg_insert
 
@@ -179,10 +179,17 @@ async def run() -> None:
     # Database
     engine, session_factory = create_db(config)
 
-    # Anthropic client + LLM analyzer
-    anthropic = AsyncAnthropic(api_key=config.anthropic_api_key)
+    # OpenRouter client + LLM analyzer
+    client = AsyncOpenAI(
+        api_key=config.openrouter_api_key,
+        base_url="https://openrouter.ai/api/v1",
+        default_headers={
+            "HTTP-Referer": "https://trading.viktorbarzin.me",
+            "X-Title": "trading-bot meet-kevin",
+        },
+    )
     analyzer = LlmAnalyzer(
-        client=anthropic,
+        client=client,
         model=config.meet_kevin_llm_model,
         prompt_version=config.meet_kevin_prompt_version,
     )
@@ -241,7 +248,7 @@ async def run() -> None:
                 except asyncio.TimeoutError:
                     pass  # Normal timeout — loop again
     finally:
-        await anthropic.close()
+        await client.close()
         await engine.dispose()
         logger.info("meet-kevin-watcher stopped gracefully")