fix: change miner authentication to use separate X-Miner-ID header instead of API key for miner identification

- Add get_miner_id() dependency to extract miner ID from X-Miner-ID header
- Update miner register and heartbeat endpoints to require both X-Miner-ID and X-Api-Key headers
- Remove miner_id from query parameters in favor of header-based extraction
- Fix miner heartbeat CLI to send proper JSON payload with inflight, status, and metadata fields
- Fix typo in MinerService: extra_metadata → extra_meta_data

apps/coordinator-api/src/app/deps.py

@@ -36,6 +36,17 @@ def require_miner_key() -> Callable[[str | None], str]:
     return validator
 
 
+def get_miner_id() -> Callable[[str | None], str]:
+    """Dependency to get miner ID from X-Miner-ID header."""
+
+    def validator(miner_id: str | None = Header(default=None, alias="X-Miner-ID")) -> str:
+        if not miner_id:
+            raise HTTPException(status_code=400, detail="X-Miner-ID header required")
+        return miner_id
+
+    return validator
+
+
 def require_admin_key() -> Callable[[str | None], str]:
     """Dependency for admin API key authentication (reads live settings)."""