fix(app): back off event stream reconnects after repeated failures

[CannonRS]

Issue for this PR

Closes #48014

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

The global event stream (server-sdk.tsx) reconnected after every failure with
the same fixed RECONNECT_DELAY_MS delay. This adds an exponential backoff:

• a consecutiveErrors counter resets on every successfully consumed event and
  increments on each catch;
• the reconnect wait becomes
  min(5000, RECONNECT_DELAY_MS * 1.5 ** min(consecutiveErrors, 8)),
  so repeated failures back off from 250 ms up to a 5 s cap, while a healthy
  stream keeps the fast cadence.

No other behaviour in the loop changes.

How did you verify your code works?

• bun typecheck in packages/app: clean.
• The change is a 5-line delta restricted to the reconnect wait; the counter is
  scoped to the loop invocation and reset on any received event, so a recovered
  stream returns to the fast path immediately.

Screenshots / recordings

N/A — not a UI change.

Fork

• Source fork: https://github.com/mQorva/OpenCode
• Diff against this fork's dev: mQorva/OpenCode@dev...event-reconnect-backoff

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR