feat(db): add database backup/restore tooling

- tooling/db-backup: copies shared settledreach.db to docs/backups/
  for git tracking (main branch only)
- tooling/db-install: restores from backup for new clones
- make db-backup / make db-install Makefile targets
- worktree-update skill runs make db-backup after merges on main

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

Makefile

@@ -1,7 +1,8 @@
 GODOT := $(shell command -v godot4 2>/dev/null || command -v godot 2>/dev/null)
 
 .PHONY: help setup build client server test lint ci ci-client ci-server clean \
-       decisions-sync decisions-coverage decisions-active decisions-orphan
+       decisions-sync decisions-coverage decisions-active decisions-orphan \
+       db-backup db-install
 
 # --- Configuration ---
 
@@ -22,6 +23,9 @@ help:
 	@echo "  make ci-server      Run server CI checks"
 	@echo "  make clean          Remove build artifacts and caches"
 	@echo ""
+	@echo "  make db-backup          Backup shared database to git (main only)"
+	@echo "  make db-install         Restore shared database from backup"
+	@echo ""
 	@echo "  make decisions-sync     Sync decisions/*.md into SQLite"
 	@echo "  make decisions-coverage Decision-to-ticket coverage by domain"
 	@echo "  make decisions-active   List active decisions"
@@ -101,6 +105,14 @@ ci-server: lint-server build-server test-server
 
 ci-client: lint-client build-client test-client
 
+# --- Database ---
+
+db-backup:
+	@tooling/db-backup
+
+db-install:
+	@tooling/db-install
+
 # --- Decisions ---
 
 decisions-sync: