auto-generate doesn't work with `verbose = true`

[lalitmee]

Description

# ~/.config/git/config
[commit]
	verbose = true

With the above config, I've observed that the automated commit message generation does not run when the commit editor is launched. The process has to be initiated manually.

Neovim Info

> nvim --version
NVIM v0.11.4
Build type: Release
LuaJIT 2.1.1741730670
Run "nvim -V1 -v" for more info

Is this intentional or expected behaviour?

[jinzhongjia]

I think this is a bug

[lalitmee]

@jinzhongjia, actually I would not consider it as a bug as I am guessing that you would have not thought about this edge case while implementing the plugin.

[lalitmee]

@jinzhongjia I have also noticed sometimes, that the model generates the commit with markdown code blocks wrapped around it. I think we can put this specific instruction of not to put the markdown code blocks in the result in the LLM Prompt

[jinzhongjia]

### 1. **Fixed auto-generation failure when `commit.verbose = true`**

**Root Cause**: When Git is configured with `commit.verbose = true`, Git adds detailed diff content at the bottom of the commit message editor (after the `# ------------------------ >8 ------------------------` separator line). These diff lines don't start with `#`, causing the plugin to mistakenly think the buffer already has user content, thus skipping auto-generation.

**Solution**:
- Added detection for the verbose diff separator line in the `should_attempt_auto_generate` function in `buffer.lua`
- Only check content before the separator line to determine if there's user-inputted commit message
- Updated `_insert_commit_message` function to ensure generated messages are inserted at the correct position (before comments and verbose diff)

### 2. **Prevent LLM output from being wrapped in markdown code blocks**

**Issue Description**: Sometimes the LLM wraps commit messages in markdown code blocks (like ````...````)

**Solution**:
- Updated the prompt with clearer instructions prohibiting markdown code blocks
- Added `_clean_commit_message` function as a post-processing step to automatically remove any potential code block wrapping
- This provides double protection: prompt guidance + output post-processing

### Modified Files

1. **`lua/codecompanion/_extensions/gitcommit/buffer.lua`**
   - Fixed verbose mode detection logic
   - Improved message insertion position determination

2. **`lua/codecompanion/_extensions/gitcommit/generator.lua`**
   - Enhanced prompt to explicitly prohibit markdown code blocks
   - Added output cleaning function

These fixes ensure the plugin works properly in `commit.verbose = true` environments and makes the generated commit message format more reliable.

I try to fix this with claude sonnet 4.5, maybe it can work

I have push it to #18

[lalitmee]

@jinzhongjia, great, will give it a try.