BACK-403 - Expose and honor task ordinal in MCP task tools (#564)

## Summary
- expose the existing ordinal field on MCP task_create and task_edit
- persist ordinal on task creation and honor ordinal-aware ordering in
MCP task_list
- show ordinal in task responses and add targeted MCP tests for schema,
persistence, ordering, and validation

## Testing
- bun test src/test/mcp-tasks.test.ts
- bunx tsc --noEmit
- bun run check src/types/index.ts src/core/backlog.ts
src/mcp/tools/tasks/handlers.ts src/mcp/utils/schema-generators.ts
src/formatters/task-plain-text.ts src/test/mcp-tasks.test.ts

Closes #562

Author: MrLesk

AGENTS.md

@@ -74,6 +74,13 @@ If you can simplify the code, do it.
 - **Task Management**: Uses markdown files in `backlog/` directory structure
 - **Workflow**: Git-integrated with task IDs referenced in commits and PRs
 
+## Agent POV
+
+- Treat Backlog.md as a shipped CLI/MCP binary that may be used from other repositories where agents cannot inspect this source tree.
+- When you decide what another agent can rely on, use only the public surface: MCP workflow resources, MCP tool descriptions/schemas, CLI help, and instruction files shipped with the project.
+- Do not assume external agents know internal implementation details, constants, or source-only conventions.
+- If a convention matters for agent behavior, document it in the public MCP/instruction surface rather than relying on source-code discovery.
+
 ## Code Standards
 
 - **Runtime**: Bun with TypeScript 5

CLAUDE.md

@@ -0,0 +1 @@
+AGENTS.md