Initial import: Slack export triage UI for Mattermost migration.

Web UI for channel/message cherry-pick, attachment preview, hydrate script,
and workspace skip presets.

Makefile

@@ -0,0 +1,15 @@
+.PHONY: help review hydrate preset-skips
+
+help: ## Show targets
+	@grep -E '^[a-zA-Z0-9_-]+:.*##' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*## "}; {printf "  \033[36m%-16s\033[0m %s\n", $$1, $$2}'
+
+review: ## Start triage UI (http://127.0.0.1:8765)
+	@chmod +x run.sh
+	@./run.sh
+
+hydrate: ## Download attachments from official Slack export URLs
+	@chmod +x scripts/hydrate-export.sh
+	@./scripts/hydrate-export.sh
+
+preset-skips: ## Apply presets/levkin-skips.json channel skips to manifest.json
+	@python3 scripts/preset-skips.py