Add in-progress status tracking for features

Implements feature locking to prevent multiple agent sessions from working
on the same feature simultaneously. This is essential for parallel agent
execution.

Database changes:
- Add `in_progress` boolean column to Feature model
- Add migration function to handle existing databases

MCP Server tools:
- Add `feature_mark_in_progress` - lock feature when starting work
- Add `feature_clear_in_progress` - unlock feature when abandoning
- Update `feature_get_next` to skip in-progress features
- Update `feature_get_stats` to include in_progress count
- Update `feature_mark_passing` and `feature_skip` to clear in_progress

Backend updates:
- Update progress.py to track and display in_progress count
- Update features router to properly categorize in-progress features
- Update WebSocket to broadcast in_progress in progress updates
- Add in_progress to FeatureResponse schema

Frontend updates:
- Add in_progress to TypeScript types (Feature, ProjectStats, WSProgressMessage)
- Update useWebSocket hook to track in_progress state

Prompt template:
- Add instructions for agents to mark features in-progress immediately
- Document new MCP tools in allowed tools section

Also fixes spec_chat_session.py to use absolute project path instead of
relative path for consistency with CLI behavior.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ui/src/hooks/useWebSocket.ts

@@ -8,6 +8,7 @@ import type { WSMessage, AgentStatus } from '../lib/types'
 interface WebSocketState {
   progress: {
     passing: number
+    in_progress: number
     total: number
     percentage: number
   }
@@ -20,7 +21,7 @@ const MAX_LOGS = 100 // Keep last 100 log lines
 
 export function useProjectWebSocket(projectName: string | null) {
   const [state, setState] = useState<WebSocketState>({
-    progress: { passing: 0, total: 0, percentage: 0 },
+    progress: { passing: 0, in_progress: 0, total: 0, percentage: 0 },
     agentStatus: 'stopped',
     logs: [],
     isConnected: false,
@@ -57,6 +58,7 @@ export function useProjectWebSocket(projectName: string | null) {
                 ...prev,
                 progress: {
                   passing: message.passing,
+                  in_progress: message.in_progress,
                   total: message.total,
                   percentage: message.percentage,
                 },