fix(daemon): throttle OpenCode capture retries for dead server ports

[proboscis]

Summary

• Implement per-run exponential backoff (10s → 60s cap) for message capture failures against dead OpenCode server endpoints
• Apply stricter backoff (2x multiplier) for ECONNREFUSED errors specifically
• Rate-limit and deduplicate log messages to avoid spam

Motivation

Connection refused errors from stale OpenCode server ports created high-volume log noise and unnecessary retry load when daemon monitoring attempted message capture against older runs whose servers had stopped.

Changes

internal/daemon/daemon.go

• Extended RunState struct with capture backoff state fields:
  • CaptureFailCount - tracks consecutive failures
  • LastCaptureFailAt - when last failure occurred
  • NextCaptureRetryAt - backoff deadline
  • LastCaptureError - for log deduplication

internal/daemon/monitor.go

• Added backoff constants: initial=10s, max=60s, factor=2x
• shouldSkipCapture() - skips capture during backoff period
• handleCaptureError() - sets backoff and logs first/new errors only
• resetCaptureBackoff() - clears state on successful capture
• calculateCaptureBackoff() - exponential backoff with ECONNREFUSED boost
• isConnectionRefused() - detects connection refused via net.OpError or string

internal/daemon/monitor_test.go

• Tests for shouldSkipCapture, calculateCaptureBackoff, handleCaptureError, resetCaptureBackoff, isConnectionRefused

Acceptance Criteria Evidence

Criterion	Evidence
Connection-refused spam reduced to bounded, periodic logs	First error logged, then debug-level only for repeats. Backoff caps at 60s.
Capture loop avoids tight retries	shouldSkipCapture() enforces NextCaptureRetryAt deadline.
Normal live OpenCode capture still works	resetCaptureBackoff() clears state on success; no changes to successful path.
Tests cover retry/backoff behavior	5 new test functions with subtests covering all backoff scenarios.

=== RUN   TestShouldSkipCapture
=== RUN   TestShouldSkipCapture/no_backoff_state_allows_capture
=== RUN   TestShouldSkipCapture/future_NextCaptureRetryAt_skips_capture
=== RUN   TestShouldSkipCapture/past_NextCaptureRetryAt_allows_capture
--- PASS: TestShouldSkipCapture (0.00s)
=== RUN   TestCalculateCaptureBackoff
=== RUN   TestCalculateCaptureBackoff/first_failure_uses_initial_backoff
=== RUN   TestCalculateCaptureBackoff/exponential_backoff_increases
=== RUN   TestCalculateCaptureBackoff/backoff_caps_at_max
--- PASS: TestCalculateCaptureBackoff (0.00s)
=== RUN   TestHandleCaptureError
=== RUN   TestHandleCaptureError/first_error_sets_backoff_state
=== RUN   TestHandleCaptureError/consecutive_errors_increase_fail_count
--- PASS: TestHandleCaptureError (0.00s)
=== RUN   TestResetCaptureBackoff
--- PASS: TestResetCaptureBackoff (0.00s)
=== RUN   TestIsConnectionRefused
--- PASS: TestIsConnectionRefused (0.00s)

Fixes: orch-427