feat(#68): per-phase granularity overrides (granularities.<phaseType>) (#595)

Closes #68. Per-phase-type granularity overrides via granularities.<phaseType>, mirroring models.<phaseType>. Includes maintainer-authorized sdk-seam reference cleanup.

docs/FEATURES.md

@@ -925,6 +925,7 @@ continues. Drift detection cannot fail verification.
 | `granularity` | enum | `standard` | `coarse`, `standard`, or `fine` |
 | `model_profile` | enum | `balanced` | `quality`, `balanced`, `budget`, or `inherit` |
 | `models.<phase_type>` | enum | (none) | Per-phase-type tier override (`planning`, `discuss`, `research`, `execution`, `verification`, `completion`). Values: `opus`, `sonnet`, `haiku`, `inherit`. Coarse phase-level tuning that wins over `model_profile` but loses to per-agent `model_overrides`. See [CONFIGURATION.md](CONFIGURATION.md#per-phase-type-models-models--added-in-v140). Added in v1.40 |
+| `granularities.<phase_type>` | enum | (none) | Per-phase-type granularity override (`planning`, `discuss`, `research`, `execution`, `verification`, `completion`). Values: `coarse`, `standard`, `fine`. Mirrors `models.<phase_type>` for granularity. See [CONFIGURATION.md](CONFIGURATION.md#core-settings). Added in v1.43 ([#68](https://github.com/open-gsd/gsd-core/issues/68)) |
 | `dynamic_routing.enabled` | boolean | `false` | Master switch for failure-tier escalation. When `true`, agents resolve to `tier_models[default_tier]` and escalate one tier on orchestrator-detected soft failure. Capped by `max_escalations`. See [CONFIGURATION.md](CONFIGURATION.md#dynamic-routing-with-failure-tier-escalation-dynamic_routing--added-in-v140). Added in v1.40 |
 | `workflow.research` | boolean | `true` | Domain research before planning |
 | `workflow.plan_check` | boolean | `true` | Plan verification loop |