feat(meta): replace sprint workflow with kanban + milestones (D-221)

Sprint-based workflow (38 sprints) replaced by kanban + milestones.
Milestones are many-to-many with tickets and can block each other.

New: /whats-next skill (dependency-driven batch selection with Si
refinement review), /pr-process skill (renamed from pr-push, adds
review comment pickup), clerk agent + pre-push hook for D-record
consistency checks.

Deleted: sprint CLI, sprint-start/sprint-plan/sprint-status skills,
team-scoped file restrictions. Si rewritten as refinement manager.
All 19 agent briefings updated from stale PROJECT_STATE.md reference
to live ticket milestone queries.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/briefings/clerk.md

@@ -0,0 +1,42 @@
+---
+title: "Clerk - Project Briefing"
+description: "Pre-push institutional guardrail — checks D-record consistency, ticket drift, decision contradictions, and Q-record surfacing before code lands"
+type: briefing
+status: active
+agent: Clerk
+updated: 2026-05-03
+---
+
+# Clerk - Project Briefing
+Last updated: 2026-05-03
+
+## Role: Pre-Push Institutional Guardrail
+
+Review branch changes before push to catch institutional drift: decision contradictions, ticket scope creep, missing D-records for new behavior, and unresolved Q-records that should block merge.
+
+## What to Check
+
+1. **D-record consistency** — do the branch changes align with referenced D-records? Does any new code or content introduce behavior that contradicts a confirmed decision?
+2. **Ticket drift** — does the work on the branch match the ticket description and acceptance criteria, or has scope crept?
+3. **Decision contradictions** — do any two D-records referenced by this branch contradict each other? Has a D-record been amended elsewhere but not reflected in the branch?
+4. **Q-record surfacing** — are there open Q-records (questions) that this branch implicitly resolves or depends on? If so, flag them for explicit resolution before merge.
+
+## Where to Find Decisions
+
+- **Decision index:** `decisions/README.md` — master index of all domain files
+- **Domain files:** `decisions/architecture.md`, `decisions/perception.md`, `decisions/content.md`, `decisions/scope.md`, `decisions/economics.md`, `decisions/process.md`
+- **Open questions:** `decisions/questions.md`, `decisions/questions-process.md`
+- **Rejected proposals:** `decisions/rejected.md`
+- **Decision DB table:**
+  ```bash
+  tooling/db/sqlite-query "SELECT id, title, status, domain FROM decisions WHERE domain = '<domain>'"
+  ```
+
+## Output
+
+Write findings to `.cache/pre-push-review.md`. End with a binary verdict:
+
+- **APPROVED** — no institutional issues found, safe to push
+- **REJECTED** — list each issue with the D/Q-record reference and what needs resolution
+
+The findings file is gitignored (lives in `.cache/`) and is consumed by the push workflow.