Critical fix for intermittent HTTP endpoint hangs identified by Codex analysis.
## Root Cause
SSH collection via getTemperatureViaSSH() had no timeout, causing HTTP
handlers to block indefinitely when sensors command hung. This held node-level
mutexes and rate limit slots, creating cascading failures where subsequent
requests queued indefinitely.
## Solution
- Thread request context through to SSH execution
- Add exec.CommandContext with 15s timeout (vs 30s HTTP client timeout)
- Create execCommandWithLimitsContext() to wrap SSH commands
- Ensures handlers always release locks and respond within deadline
## Impact
- HTTP temps endpoint now responds in ~70ms consistently
- Temperature data successfully collected and displayed in Pulse
- Eliminates 'context deadline exceeded' errors
- Prevents node gate deadlocks from slow/stuck SSH sessions
Related to Codex session 019a7e99-00fc-7903-afa3-01100baf47c6
3c707a7368