feat: add escalation judge skill

[liyitong10086]

Adds an escalation-judge runx skill package for support-thread escalation decisions.

Included:

• skills/escalation-judge/SKILL.md and X.yaml
• Three inline harness cases covering escalation, no-change stop, and missing-policy refusal
• Fixtures and local harness evidence
• Graph runner that reads prior case projection, grounds severity/churn matches in policy, appends one case event only when escalation is warranted, and emits a typed escalation packet without dispatching Slack/email

Local verification:

• runx-cli 0.6.14 skill inspect passed
• runx-cli 0.6.13 local harness passed 3/3 on Windows because 0.6.14 Windows receipt store returns os error 87 on this host