Simplify Leader skill guidance for worker name canonicality in task assignment

## Problem

The Leader LLM sometimes uses the CLI `.name` field (which may include deployment prefixes like `magic-cn-...-worker-issue-resolver`) or attempts to manually strip prefixes when filling `assignedTo` / `assigned_to`. This produces values that do not match the Worker's Matrix localpart, causing task routing failures.

The current skill documents address this with extensive defensive warnings (❌ lists, mandatory lookup steps, common-mistake tables). These are verbose and distract from the core rule.

## Goal

Replace the defensive documentation pattern with a concise positive instruction: use the Matrix localpart, here is an example, here is where to find it.

## Scope

- `manager/agent/team-leader-agent/skills/project-management/SKILL.md`
- `manager/agent/team-leader-agent/skills/project-management/references/dag-execution.md`
- `manager/agent/team-leader-agent/skills/task-management/SKILL.md`

No code or validation changes — skill prompt simplification only.

## Acceptance Criteria

- [x] DAG `assignedTo` guidance is a single positive description with example
- [x] Loop `assignedTo` guidance references the same rule without duplication
- [x] Task management "Worker Name" section is concise (no ❌ lists, no mandatory bash snippets, no mistake tables)
- [x] All three files still direct the Leader to extract the localpart from `matrixUserID` via `hiclaw get workers`