refactor: reorganize project structure and update configurations

- Move migrations/ to database/schema/ for clarity on database schema definitions
- Move sqlc.yaml to internal/database/ to group with database code
- Move static/ to cmd/server/static/ to co-locate with server
- Update all configuration files and documentation
- Follow Go project conventions for better organization

internal/database/sqlc.yaml

@@ -0,0 +1,17 @@
+version: "2"
+sql:
+  - engine: "postgresql"
+    schema: "database/schema"
+    queries: "internal/database/queries"
+    gen:
+      go:
+        package: "database"
+        out: "internal/database"
+        sql_package: "pgx/v5"
+        emit_db_tags: true
+        emit_prepared_queries: true
+        emit_interface: true
+        emit_exact_table_names: true
+        emit_empty_slices: true
+        emit_exported_queries: true
+        emit_json_tags: true