docs: enhance custom modes documentation with model persistence details

Author: hannesrudolph

docs/basic-usage/using-modes.md

@@ -2,6 +2,10 @@
 
 Modes in Roo Code are specialized personas that tailor the assistant's behavior to your current task. Each mode offers different capabilities, expertise, and access levels to help you accomplish specific goals.
 
+:::info Model Persistence
+Each mode remembers the last model you used with it. When switching modes, Roo automatically selects the model you previously set for that mode—allowing you to maintain different preferred models for different types of tasks without manual reconfiguration.
+:::
+
 ## Why Use Different Modes?
 
 - **Task specialization:** Get precisely the type of assistance you need for your current task

docs/features/custom-modes.md

@@ -1,6 +1,6 @@
 # Custom Modes
 
-Roo Code allows you to create **custom modes** to tailor Roo's behavior to specific tasks or workflows. Custom modes can be either **global** (available across all projects) or **project-specific** (defined within a single project).
+Roo Code allows you to create **custom modes** to tailor Roo's behavior to specific tasks or workflows. Custom modes can be either **global** (available across all projects) or **project-specific** (defined within a single project). Each mode—including custom ones—remembers the last model you used with it, automatically selecting that model when you switch to the mode. This lets you maintain different preferred models for different types of tasks without manual reconfiguration.
 
 :::info Mode-Specific Instruction File Locations
 You can provide instructions for custom modes using dedicated files or directories within your workspace. This allows for better organization and version control compared to only using the JSON `customInstructions` property.