chore: remove Backlog.md task system and backlog directory

- Delete Backlog.md and all backlog/ task files
- Remove Backlog.md MCP workflow instructions from AGENTS.md
- Drop "backlog history" from change-verification shim compatibility note

AGENTS.md

@@ -64,32 +64,3 @@ Start here, then leave this file.
 - CI red: `gh run list/view`, rerun, fix, repeat until green
 - TypeScript: keep files small; follow existing patterns
 - Swift: use workspace helper/daemon; validate `swift build` + tests
-
-<!-- BACKLOG.MD MCP GUIDELINES START -->
-
-<CRITICAL_INSTRUCTION>
-
-## BACKLOG WORKFLOW INSTRUCTIONS
-
-This project uses Backlog.md MCP for all task and project management activities.
-
-**CRITICAL GUIDANCE**
-
-- If your client supports MCP resources, read `backlog://workflow/overview` to understand when and how to use Backlog for this project.
-- If your client only supports tools or the above request fails, call `backlog.get_workflow_overview()` tool to load the tool-oriented overview (it lists the matching guide tools).
-
-- **First time working here?** Read the overview resource IMMEDIATELY to learn the workflow
-- **Already familiar?** You should have the overview cached ("## Backlog.md Overview (MCP)")
-- **When to read it**: BEFORE creating tasks, or when you're unsure whether to track work
-
-These guides cover:
-- Decision framework for when to create tasks
-- Search-first workflow to avoid duplicates
-- Links to detailed guides for task creation, execution, and finalization
-- MCP tools reference
-
-You MUST read the overview resource to understand the complete workflow. The information is NOT summarized here.
-
-</CRITICAL_INSTRUCTION>
-
-<!-- BACKLOG.MD MCP GUIDELINES END -->