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>

.claude/rules/ticket-cli.md

@@ -25,10 +25,27 @@ tooling/db/ticket create <type> <title> [--parent N] [--priority P] [--decision
 
 # Read
 tooling/db/ticket show <id>
-tooling/db/ticket list [--sprint N] [--team T] [--status S]
+tooling/db/ticket list [--milestone N] [--team T] [--status S]
 
 # Update
 tooling/db/ticket assign <id> <agent>
+
+# Dependencies
+tooling/db/ticket deps <id>
+tooling/db/ticket dep add <blocker_id> <blocked_id>
+tooling/db/ticket dep rm <blocker_id> <blocked_id>
+
+# WIP
+tooling/db/ticket wip
+
+# Milestones
+tooling/db/ticket milestone list [--status S]
+tooling/db/ticket milestone create <name> [--description TEXT] [--phase N]
+tooling/db/ticket milestone link <ticket_id> <milestone_id>
+tooling/db/ticket milestone unlink <ticket_id> <milestone_id>
+tooling/db/ticket milestone complete <milestone_id>
+tooling/db/ticket milestone show <milestone_id>
+tooling/db/ticket milestone dep <blocker_id> <blocked_id>
 ```
 
 ## Key rules
@@ -37,3 +54,4 @@ tooling/db/ticket assign <id> <agent>
 - **Quote the title** — always wrap in double quotes to handle spaces
 - **Never use `sqlite3` CLI** — it crashes (std::bad_alloc). Use `tooling/db/sqlite-query` or `tooling/db/sqlite-exec` for raw SQL
 - **Verify after create** — run `tooling/db/ticket show <id>` to confirm the title is clean
+- **Milestones are many-to-many** — a ticket can be linked to multiple milestones via `milestone link`