docs: Couple of random anon leftovers (#46732)

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES/


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

## Documentation

* Updated project variables guidance to include publishable and secret
keys alongside existing options.
* Updated code examples across multiple frameworks to use publishable
keys instead of anon keys.
* Updated tool descriptions to reflect publishable key terminology.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/docs/app/contributing/content.mdx

@@ -354,7 +354,7 @@ If your image has alternate light and dark versions, or you want to make it zoom
 
 ### Project Variables
 
-Some guides and tutorials will require that users copy their Supabase project URL and anon key. You can provide those inline if the user is signed in:
+Some guides and tutorials will require that users copy their Supabase project URL and publishable or secret key. You can provide those inline if the user is signed in:
 
 ```mdx
 <ProjectConfigVariables variable="url" />

apps/docs/content/guides/ai-tools/mcp.mdx

@@ -52,7 +52,7 @@ The Supabase MCP server provides tools organized into feature groups. All groups
 ### Development
 
 - `get_project_url` - Get the API URL for a project
-- `get_publishable_keys` - Get anon/public keys
+- `get_publishable_keys` - Get publishable and legacy anon API keys for a project
 - `generate_typescript_types` - Generate TypeScript types from schema
 
 ### Edge Functions

apps/docs/content/guides/auth/third-party/clerk.mdx

@@ -77,7 +77,7 @@ import Supabase
 
 let supabase = SupabaseClient(
   supabaseURL: URL(string: "https://project-ref.supabase.io")!,
-  supabaseKey: "supabase.anon.key",
+  supabaseKey: "supabase.publishable.key",
   options: SupabaseClientOptions(
     auth: SupabaseClientOptions.AuthOptions(
       accessToken: {

apps/docs/content/guides/getting-started/quickstarts/flutter.mdx

@@ -73,7 +73,7 @@ hideToc: true
 
         await Supabase.initialize(
           url: 'YOUR_SUPABASE_URL',
-          anonKey: 'YOUR_SUPABASE_PUBLISHABLE_KEY',
+          publishableKey: 'YOUR_SUPABASE_PUBLISHABLE_KEY',
         );
         runApp(MyApp());
       }