GH-79: feat(core): add optional Logger to PollerDeps — poller logs through injected logger

[alekspetrov]

Summary

Automated PR created by Pilot for task GH-79.

Closes #79

Changes

GitHub Issue #79: feat(core): add optional Logger to PollerDeps — poller logs through injected logger

Problem

sdkcore.PollerDeps has no Logger field, so the poller loop in sdk/integrations/github (and any code it calls) logs through slog.Default(). Consumers embedding the poller cannot attribute its log lines.

Live incident (qf-studio/pilot, 2026-07-06): the SDK github poller failed every poll for ~25 minutes with msg="Failed to fetch issues" 401 errors carrying no component= tag — the operator could not tell which of nine pollers was failing. The consumer-side fix (qf-studio/pilot PR #3919) tags everything the consumer logs itself, but the poller's internal lines stay untagged until the SDK accepts a logger.

Change

1. Add Logger *slog.Logger to sdkcore.PollerDeps. Semantics: nil → fall back to slog.Default() (zero behavior change for existing consumers).
2. sdk/integrations/github poller stores the resolved logger at construction and uses it for ALL its log lines (poll loop, dispatch, retry scheduler, board sync paths). Grep for slog. / p.logger in sdk/integrations/github/poller.go — every line goes through the injected logger.
3. Golden lock: sdk/core is API-locked via TestPublicAPILocked. Adding the field is additive — re-bless with go test ./sdk/core/... -update and commit the regenerated golden. Do not remove or rename existing fields.

Acceptance

• PollerDeps{} (nil Logger) → identical behavior/output to today.
• Non-nil Logger receives every poller-originated log line; nothing from the poller reaches slog.Default() when a Logger is set.
• Golden file updated additive-only; TestPublicAPILocked green.
• Table-driven test: construct poller with a captured slog handler, run one poll cycle against a stub, assert lines arrive on the injected handler.

Refs

• qf-studio/pilot PR #3919 (consumer-side fail-loud fix; documents this gap)
• qf-studio/pilot TASK-368 M7 4d ledger