tasks: decompose Phase 0a ADR foundation and mark prior tasks completed

Add 10 new tasks under tasks/architecture/ for Phase 0a (ADR writing):
- 9 ADR tasks (026-034) with dependency-ordered structure
- 1 review checkpoint task before Phase 0b spec writing

ADR dependency graph (3 generations):
  Gen 1 (parallel): 026, 029, 030, 031, 032, 034
  Gen 2 (depends on 029): 027, 028
  Gen 3 (depends on 027+028): 033
  Gen 4: review checkpoint

Also mark all 34 prior implementation tasks as completed — they
were finished but still showing as pending in the taskgraph.

tasks/architecture/adr-034-head-worker-terminology.md

@@ -0,0 +1,41 @@
+---
+id: architecture/adr-034-head-worker-terminology
+name: Write ADR-034 — Head/worker terminology
+status: pending
+depends_on: []
+scope: single
+risk: trivial
+impact: project
+level: implementation
+---
+
+## Description
+
+Write ADR-034 formalizing the decision to use head/worker terminology instead of hub/spoke throughout the project.
+
+This decision has already been applied in practice — `call-protocol.md`, `auth.md`, `open-questions.md`, and `napi-and-pubsub.md` were all updated to head/worker. The existing ADRs (024, 025) retain their original hub/spoke language because ADRs are historical records. ADR-018 is noted as superseded/extended by ADR-024 and the three-layer model.
+
+The ADR exists to formally record the decision so future contributors understand why and can reference it.
+
+## Acceptance Criteria
+
+- [ ] `docs/architecture/decisions/034-head-worker-terminology.md` exists
+- [ ] ADR follows the established format (Status, Context, Decision, Consequences, References)
+- [ ] Context explains why hub/spoke is being replaced (mesh topologies, a head is also a worker)
+- [ ] Decision states: head/worker everywhere in new specs and code; ADRs retain original language as historical records
+- [ ] Consequences note: natural mesh formation, consistency with integration plan terminology
+- [ ] References: integration-plan.md, ADR-024, ADR-025
+
+## References
+
+- docs/research/integration-plan.md — Phase 0 ADR 034 entry, inconsistencies section item 1
+- docs/architecture/decisions/024-bidirectional-call-protocol.md — uses hub/spoke historically
+- docs/architecture/decisions/025-handler-spec-separation.md — uses hub/spoke historically
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion