Bring "Compaction is skipped" back (removed in 1.89.0)

## Problem
IDE plugin now auto-clears chat history when context hits 100% and doesn't allow for an overflow when compacting is also not a desired outcome.

## Steps to reproduce the issue
In 1.89.0 get past 100% context without having Allowed compacting of chat and the plugin will now clear ALL chat history, completely resetting any progress made.

## Expected behavior
When dealing with complex code it is often more preferable to have specifics in more recent chat history than compacting the entire entire session. The overflow allows for debugging to continue systematically without compacting forcing the problem and progress to be summarized (and often incorrectly re-framed by the AI).

## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS: Darwin arm64 24.6.0
- Visual Studio Code version: 1.103.1
- AWS Toolkit version:
- Amazon Q version: 1.89.0 (I've reverted to 1.88.0 to avoid this forced auto-clear)

Start by reproducing the overflow in Amazon Q 1.89.0 with chat compaction disabled, then trace the chat-history overflow and compaction decision paths. Done means declining compaction no longer clears the entire conversation, while the existing compaction behavior remains available when requested.

Written by the indexing model from the issue text.