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/go-api/contract.md

@@ -1,6 +1,6 @@
 # Contract: REST API Conventions (Go Web Applications)
 
-Version: 1.0
+Version: 1.1
 
 ## URL Naming
 
@@ -82,12 +82,5 @@ GET /api/db-status → 200 {"ok": true} or 500 {"ok": false, "error": "..."}
 
 ## Async Actions
 
-For long-running operations return immediately with a task reference:
-
-```
-POST /api/pricelists/create → 202 {"task_id": "abc123"}
-GET  /api/tasks/abc123      → 200 {"status": "running", "progress": 42, "message": "Processing..."}
-GET  /api/tasks/abc123      → 200 {"status": "success", "result": {...}}
-```
-
-See `go-background-tasks/contract.md` for full task contract.
+Long-running operations return `202 {"task_id": "..."}` immediately and the client polls
+`GET /api/tasks/:id`. Full flow, statuses, and task struct: `go-background-tasks` contract.