Fix Board project loading when gateway is unavailable

[Kaguya-19]

Summary

• add a bounded gateway wait for Board project/session reads
• fall back to the local ~/.pilotdeck/projects index when the gateway is unavailable
• keep chat/task execution dependent on the gateway while allowing the Board/history list to render
• add a regression test for loading Board project data from disk when gateway connection fails

Verification

• npm --prefix ui test -- projects.test.js pilotdeck-bridge.test.js routes/gateway.test.js routes/config.test.js
• pnpm exec tsc -p tsconfig.json --noEmit
• git diff --check
• manually verified /api/projects and /api/projects/general/sessions?limit=2 return 200 when PILOTDECK_GATEWAY_URL points at an unavailable gateway
• manually verified normal npm run dev gateway health and /api/projects return 200