Fix namespaced model table names in upgrade generator (#398)

## Description

This PR fixes issue #397 where the upgrade generator produces invalid
table names for namespaced models.

## Problem

When using custom model names with namespaces (like `Assistant::Chat`,
`Assistant::Message`, etc.) and running the upgrade generator:

```bash
rails g ruby_llm:upgrade_to_v1_7 chat:Assistant::Chat message:Assistant::Message
```

The migration would generate invalid table names like `:assistant/chats`
instead of `:assistant_chats`.

## Solution

The issue was that the generator was using `.tableize` which produces
forward slashes for namespaced models. This has been fixed by using
`.underscore.pluralize.tr('/', '_')` which properly converts namespaced
model names to valid table names.

### Changes:
- Added `table_name_for` helper method that correctly handles namespaced
models
- Added helper methods for each model type (`chat_table_name`,
`message_table_name`, etc.)
- Updated migration template to use the new helper methods instead of
`.tableize`

## Testing

Tested with namespaced models to confirm:
- `Assistant::Chat` → `assistant_chats` ✓
- `Assistant::Message` → `assistant_messages` ✓
- `Assistant::ToolCall` → `assistant_tool_calls` ✓
- `Assistant::Model` → `assistant_models` ✓

Regular models continue to work as expected:
- `Chat` → `chats` ✓
- `Message` → `messages` ✓

Fixes #397

Author: willcosgrove

lib/generators/ruby_llm/upgrade_to_v1_7/templates/migration.rb.tt

@@ -6,33 +6,33 @@ class MigrateToRubyLLMModelReferences < ActiveRecord::Migration<%= migration_ver
 
     # Then check for any models in existing data that aren't in models.json
     say_with_time "Checking for additional models in existing data" do
-      collect_and_create_models(chat_class, :<%= chat_model_name.tableize %>, model_class)
-      collect_and_create_models(message_class, :<%= message_model_name.tableize %>, model_class)
+      collect_and_create_models(chat_class, :<%= chat_table_name %>, model_class)
+      collect_and_create_models(message_class, :<%= message_table_name %>, model_class)
       model_class.count
     end
 
     # Migrate foreign keys
-    migrate_foreign_key(:<%= chat_model_name.tableize %>, chat_class, model_class, :<%= model_model_name.underscore %>)
-    migrate_foreign_key(:<%= message_model_name.tableize %>, message_class, model_class, :<%= model_model_name.underscore %>)
+    migrate_foreign_key(:<%= chat_table_name %>, chat_class, model_class, :<%= model_model_name.underscore %>)
+    migrate_foreign_key(:<%= message_table_name %>, message_class, model_class, :<%= model_model_name.underscore %>)
   end
 
   def down
     # Remove foreign key references
-    if column_exists?(:<%= message_model_name.tableize %>, :<%= model_model_name.underscore %>_id)
-      remove_reference :<%= message_model_name.tableize %>, :<%= model_model_name.underscore %>, foreign_key: true
+    if column_exists?(:<%= message_table_name %>, :<%= model_model_name.underscore %>_id)
+      remove_reference :<%= message_table_name %>, :<%= model_model_name.underscore %>, foreign_key: true
     end
 
-    if column_exists?(:<%= chat_model_name.tableize %>, :<%= model_model_name.underscore %>_id)
-      remove_reference :<%= chat_model_name.tableize %>, :<%= model_model_name.underscore %>, foreign_key: true
+    if column_exists?(:<%= chat_table_name %>, :<%= model_model_name.underscore %>_id)
+      remove_reference :<%= chat_table_name %>, :<%= model_model_name.underscore %>, foreign_key: true
     end
 
     # Restore original model_id string columns
-    if column_exists?(:<%= message_model_name.tableize %>, :model_id_string)
-      rename_column :<%= message_model_name.tableize %>, :model_id_string, :model_id
+    if column_exists?(:<%= message_table_name %>, :model_id_string)
+      rename_column :<%= message_table_name %>, :model_id_string, :model_id
     end
 
-    if column_exists?(:<%= chat_model_name.tableize %>, :model_id_string)
-      rename_column :<%= chat_model_name.tableize %>, :model_id_string, :model_id
+    if column_exists?(:<%= chat_table_name %>, :model_id_string)
+      rename_column :<%= chat_table_name %>, :model_id_string, :model_id
     end
   end
 
@@ -134,4 +134,4 @@ class MigrateToRubyLLMModelReferences < ActiveRecord::Migration<%= migration_ver
       model_class.find_by(model_id: model_id)
     end
   end
-end
+end

lib/generators/ruby_llm/upgrade_to_v1_7_generator.rb

@@ -45,18 +45,28 @@ def parse_model_mappings
       @model_names
     end
 
+    def table_name_for(model_name)
+      # Convert namespaced model names to proper table names
+      # e.g., "Assistant::Chat" -> "assistant_chats" (not "assistant/chats")
+      model_name.underscore.pluralize.tr('/', '_')
+    end
+
     %i[chat message tool_call model].each do |type|
       define_method("#{type}_model_name") do
         @model_names ||= parse_model_mappings
         @model_names[type]
       end
+
+      define_method("#{type}_table_name") do
+        table_name_for(send("#{type}_model_name"))
+      end
     end
 
     def create_migration_file
       # First check if models table exists, if not create it
-      unless table_exists?(model_model_name.tableize)
+      unless table_exists?(table_name_for(model_model_name))
         migration_template 'create_models_migration.rb.tt',
-                           "db/migrate/create_#{model_model_name.tableize}.rb",
+                           "db/migrate/create_#{table_name_for(model_model_name)}.rb",
                            migration_version: migration_version,
                            model_model_name: model_model_name