fix: add filesystem fallbacks for multiple trajectory loading

[khaliqgant]

Summary

• Added filesystem fallbacks in trajectory integration to support multiple active trajectories
• Merges active-dir files with index.json so all active trajectories display even if index is stale
• Fixes issue where only single trajectory was loading in dashboard

Changes

• Modified src/trajectory/integration.ts
• Added helper functions: getCurrentPhaseFromTrajectory, listActiveTrajectoryFiles, findActiveTrajectoryPathById
• Updated getTrajectoryStatus, listTrajectorySteps, getTrajectoryHistory to use filesystem fallbacks
• Improves robustness when index.json is out of sync with active trajectories on disk

Related

• Fixes: Dashboard showing only single trajectory instead of all active ones
• Previous attempt: commit 56b1c82

Testing

• Verify multiple active trajectories now display in dashboard
• Confirm trajectory status, steps, and history are correctly merged from active-dir