feat: add interview-coach skill with Dex-native vault integration

[michrwright]

Added .claude/skills/interview-coach/SKILL.md — full interview coaching lifecycle skill with Dex-native vault integration

What this adds

A high-rigor interview coaching skill that lives natively in Dex — covering the full interview lifecycle from research through to negotiation.

Why it belongs in Dex

Dex already holds the career evidence, proof points, and relationship context that standalone interview coaching tools have to ask for from scratch. This skill reads from the vault first — seeding the storybank from existing career files, pulling interviewer context from person pages, and using QMD for semantic achievement search. The result is a coaching session that starts with your actual history, not a blank slate.

This sits naturally alongside /career-coach and /resume-builder as a third pillar of career support — activated when there's an interview in the diary.

What it does

• Full lifecycle support: research → prep → mock interview → transcript analysis → debrief → negotiation
• 5-dimension scoring rubric: Substance, Structure, Relevance, Credibility, Differentiation
• Storybank management with STAR details, earned secrets, and use tracking
• Session persistence via coaching_state.md (survives across conversations)
• Drill progression and calibration engine
• Dex-native: reads from 05-Areas/Career/, 05-Areas/Opportunities/, 05-Areas/People/External/ before asking the user

Credit

Core rubric and skill architecture adapted from noamseg/interview-coach-skill (MIT licensed). Dex integration layer and vault-aware enhancements added.

How to test

1. Run /interview-coach with a transcript or just say kickoff
2. If career files exist in the vault, the storybank seeds automatically
3. prep [company] checks 05-Areas/Opportunities/ and 05-Areas/People/External/ before asking