feat(frontend): Refactor Kanban board to focus on Story management

Refactored the Kanban board from a mixed Epic/Story/Task view to focus exclusively on Stories, which are the right granularity for Kanban management.

Changes:
- Created StoryCard component with Epic breadcrumb, priority badges, and estimated hours display
- Updated KanbanColumn to use Story type and display epic names
- Created CreateStoryDialog for story creation with epic selection
- Added useProjectStories hook to fetch all stories across epics for a project
- Refactored Kanban page to show Stories only with drag-and-drop status updates
- Updated SignalR event handlers to focus on Story events only
- Changed UI text from 'New Issue' to 'New Story' and 'update issue status' to 'update story status'
- Implemented story status change via useChangeStoryStatus hook

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/api/pm.ts

@@ -15,8 +15,10 @@ import type {
 // ==================== Epics API ====================
 export const epicsApi = {
   list: async (projectId?: string): Promise<Epic[]> => {
-    const params = projectId ? { projectId } : undefined;
-    return api.get('/api/v1/epics', { params });
+    if (!projectId) {
+      throw new Error('projectId is required for listing epics');
+    }
+    return api.get(`/api/v1/projects/${projectId}/epics`);
   },
 
   get: async (id: string): Promise<Epic> => {
@@ -47,8 +49,10 @@ export const epicsApi = {
 // ==================== Stories API ====================
 export const storiesApi = {
   list: async (epicId?: string): Promise<Story[]> => {
-    const params = epicId ? { epicId } : undefined;
-    return api.get('/api/v1/stories', { params });
+    if (!epicId) {
+      throw new Error('epicId is required for listing stories');
+    }
+    return api.get(`/api/v1/epics/${epicId}/stories`);
   },
 
   get: async (id: string): Promise<Story> => {
@@ -79,8 +83,10 @@ export const storiesApi = {
 // ==================== Tasks API ====================
 export const tasksApi = {
   list: async (storyId?: string): Promise<Task[]> => {
-    const params = storyId ? { storyId } : undefined;
-    return api.get('/api/v1/tasks', { params });
+    if (!storyId) {
+      throw new Error('storyId is required for listing tasks');
+    }
+    return api.get(`/api/v1/stories/${storyId}/tasks`);
   },
 
   get: async (id: string): Promise<Task> => {