feat(prompts): implement customizable commit message prompts

- Added a new section in the UI for customizing commit message prompts.
- Integrated a system prompt for AI-generated commit messages, allowing users to define their own instructions.
- Updated the backend to merge custom prompts with default settings for commit message generation.
- Enhanced the commit message generation logic to utilize the effective system prompt based on user settings.

libs/prompts/src/index.ts

@@ -41,6 +41,8 @@ export {
   DEFAULT_BACKLOG_PLAN_USER_PROMPT_TEMPLATE,
   DEFAULT_BACKLOG_PLAN_PROMPTS,
   DEFAULT_ENHANCEMENT_PROMPTS,
+  DEFAULT_COMMIT_MESSAGE_SYSTEM_PROMPT,
+  DEFAULT_COMMIT_MESSAGE_PROMPTS,
   DEFAULT_PROMPTS,
 } from './defaults.js';
 
@@ -50,6 +52,7 @@ export {
   mergeAgentPrompts,
   mergeBacklogPlanPrompts,
   mergeEnhancementPrompts,
+  mergeCommitMessagePrompts,
   mergeAllPrompts,
 } from './merge.js';
 
@@ -59,4 +62,5 @@ export type {
   ResolvedAgentPrompts,
   ResolvedBacklogPlanPrompts,
   ResolvedEnhancementPrompts,
+  ResolvedCommitMessagePrompts,
 } from '@automaker/types';