feat: add blockchain RPC blocks-range endpoint and marketplace bid listing

Blockchain Node:
- Replace /blocks (pagination) with /blocks-range (height range query)
- Add start/end height parameters with 1000-block max range validation
- Return blocks in ascending height order instead of descending
- Update metrics names (rpc_get_blocks_range_*)
- Remove total count from response (return start/end/count instead)

Coordinator API:
- Add effective_url property to DatabaseConfig (SQLite/PostgreSQL defaults

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

@@ -18,6 +18,19 @@ class DatabaseConfig(BaseSettings):
     max_overflow: int = 20
     pool_pre_ping: bool = True
     
+    @property
+    def effective_url(self) -> str:
+        """Get the effective database URL."""
+        if self.url:
+            return self.url
+        
+        # Default SQLite path
+        if self.adapter == "sqlite":
+            return "sqlite:///./coordinator.db"
+        
+        # Default PostgreSQL connection string
+        return f"{self.adapter}://localhost:5432/coordinator"
+    
     model_config = SettingsConfigDict(
         env_file=".env",
         env_file_encoding="utf-8",