custom ecb is dynamic table and not system table from now on2

common/proto/table_definition.proto

@@ -14,6 +14,10 @@ service TableDefinition {
   // Also inserts metadata and default validation rules. Entirely transactional.
   rpc PostTableDefinition(PostTableDefinitionRequest) returns (TableDefinitionResponse);
 
+  // Explicitly creates the optional administrator-managed exchange-rate table
+  // in an existing profile. The server owns its core shape and constraints.
+  rpc CreateCustomExchangeRatesTable(CreateCustomExchangeRatesTableRequest) returns (CreateCustomExchangeRatesTableResponse);
+
   // Creates a regular user-table bundle from the restricted komp_ac_fields
   // contract embedded in a Typst invoice template. This is invoked explicitly
   // by the user; templates do not provision tables merely by existing.
@@ -53,14 +57,23 @@ service TableDefinition {
   rpc DeleteTable(DeleteTableRequest) returns (DeleteTableResponse);
 }
 
+message CreateCustomExchangeRatesTableRequest {
+  string profile_name = 1;
+}
+
+message CreateCustomExchangeRatesTableResponse {
+  int64 table_definition_id = 1;
+  bool created = 2;
+}
+
 // Defines the input for creating a new table definition.
 message PostTableDefinitionRequest {
   // Table name to create inside the target profile.
   // Must be lowercase, alphanumeric with underscores,
   // start with a letter, and be <= 63 chars.
-  // Forbidden names: "id", "deleted", "created_at", "row_revision" -- the
-  // system columns, which share one namespace with table names wherever the
-  // two are named side by side. The "_id" suffix is allowed.
+  // Forbidden names include the system columns and tables owned by dedicated
+  // server operations, such as "custom_exchange_rates". The "_id" suffix is
+  // allowed.
   string table_name = 1;
 
   // The table's columns, including its links and stored linked projections.