feat: expand magic prompts coverage and split generation prompts (#835)

- Add configurable visible/instructions prompt families for commit/PR generation, PR checks/comments flows, and git conflict resolution helpers.
- Refactor prompt sending to explicit visible + synthetic parts instead of newline-based splitting, with legacy override migration for old keys.
- Polish Magic Prompts settings UX with grouped sidebar entries, tooltip-based descriptions, AI icon, and validation that visible prompts cannot be empty across web and VS Code runtimes.

packages/ui/src/stores/useMagicPromptsStore.ts

@@ -0,0 +1,20 @@
+import { create } from 'zustand';
+
+type MagicPromptsState = {
+  selectedPromptId: string;
+  setSelectedPromptId: (id: string) => void;
+};
+
+const DEFAULT_PROMPT_ID = 'git.commit.generate';
+
+export const useMagicPromptsStore = create<MagicPromptsState>((set) => ({
+  selectedPromptId: DEFAULT_PROMPT_ID,
+  setSelectedPromptId: (id) => {
+    set((state) => {
+      if (state.selectedPromptId === id) {
+        return state;
+      }
+      return { selectedPromptId: id };
+    });
+  },
+}));