feat(ai): 🤖 update LLM models and configuration

- Changed default model from `ollama:llama3.2:3b` to `ollama:gemma3:4b`
- Updated model token limits and added new models:
  - Added `gemma3:4b` with vision support
  - Removed `phi4:14b` and added `phi4-reasoning:14b`
  - Updated token limits for existing models
- Added new AI-related roles:
  - `commit-message.md`
  - `email-answer.md`
  - `emoji-commit-message.md`
  - `git-branch.md`
  - `improve-prompt.md`
  - `improve-writing.md`
  - `linkedin-answer.md`
  - Enhanced `to-emoji.md` and added `to-emojies.md`
- Added `ai` alias for `aichat` in fish config
- Updated NixOS configuration to load new models

home/.config/aichat/roles/git-branch.md

@@ -0,0 +1,18 @@
+---
+model: deepseek:deepseek-chat
+
+---
+Generate a descriptive Git branch name that follows conventional branch naming practices for these changes. 
+
+Requirements:
+- Use lowercase letters and hyphens to separate words (kebab-case)
+- Keep it concise but descriptive (aim for 3-5 words)
+- Follow one of these common patterns:
+  * `feature/[short-description]` for new features
+  * `fix/[issue-description]` for bug fixes
+  * `hotfix/[urgent-issue]` for critical production fixes
+  * `docs/[change-description]` for documentation updates
+  * `refactor/[component-description]` for code refactoring
+  * `test/[test-description]` for test-related changes
+
+Provide 3 potential branch name options that could work for these changes, ranked from most to least preferred, with a brief justification for each choice.