Deduplicate overlapping rules across contracts

Each rule now has one owning contract; others point to it:
validation and multi-step rules live in forms-validation (modal-workflows
references them), pagination metadata lives in go-api (table-management
references it), the async task flow lives in go-background-tasks (go-api
references it), backup git-safety checks live in backup-management
(go-database references it). Remove the leftover Vapor/Aqua baseline
mention and stale kit/patterns paths, compress the batch-file-upload ADR
narrative, and drop content-free pattern READMEs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

rules/patterns/import-export/README.md

@@ -1,15 +1,6 @@
-# Import / Export Pattern
+# Import / Export Pattern Notes
 
-Canonical file transfer UX patterns for Go web applications:
-
-- file import forms (CSV/JSON and similar)
-- validation preview tables before confirm
-- confirm step with human-readable summary
-- export controls (format + scope + options)
-- predictable file download behavior and filenames
-
-This pattern covers UI and UX contracts. Business-specific validation and file schemas remain in
-the host project's own architecture docs.
+This file keeps examples. The normative rules live in `contract.md`.
 
 ## Export Handler Sketch