Pin DeepSeek child display name

[erickkkyt]

What changed

• Pin the first native child nickname candidate to DeepSeek.
• Verify agent_nickname = DeepSeek in Codex thread metadata during native routing tests.
• Preserve byte-compatible legacy role migration behavior.
• Document Codex ordinal suffixes and the current generic-icon limitation.
• Replace the misleading direct-mention smoke test with a parent-to-child delegation prompt.

Why

Codex used its default scientist nickname pool when the role did not specify nickname candidates, so a correctly routed DeepSeek child appeared as Maxwell, Mendel, or another generated name.

Validation

• Python 3.9: 48 tests passed
• Python 3.12: 48 tests passed
• Skill structure validation passed
• JSON, bytecode, diff, and secret checks passed
• Local repair completed
• Two fresh native child tasks recorded provider deepseek, model deepseek-v4-flash, role DeepSeek, nickname DeepSeek, and returned the exact child verification token