feat: add spec-interview skill for requirement gathering (#103)

.claude/skills/spec-interview/SKILL.md

@@ -0,0 +1,51 @@
+---
+name: spec-interview
+description: Conduct an in-depth interview to gather requirements and write a detailed spec
+---
+
+## Overview
+
+Conduct a thorough interview using `AskUserQuestion` to deeply understand a feature, system, or idea before writing a specification document.
+
+## Core Principles
+
+1. **Use your judgment** - Adapt question depth and focus based on the topic. A small UI change needs different questions than a new authentication system.
+
+2. **Ask non-obvious questions** - Skip surface-level questions. Probe for:
+   - Hidden assumptions the user hasn't articulated
+   - Edge cases they haven't considered
+   - Tradeoffs they're implicitly making
+   - Constraints they forgot to mention
+   - Failure modes and recovery paths
+
+3. **Follow interesting threads** - When an answer reveals complexity or uncertainty, dig deeper before moving on.
+
+4. **Challenge gently** - Ask "what if X fails?" or "why not Y instead?" to stress-test the design.
+
+5. **Know when to stop** - End the interview when you have enough clarity to write a useful spec. Not every topic needs exhaustive coverage.
+
+## Question Areas (use as needed, not as a checklist)
+
+- **Problem & motivation**: Why now? What's the cost of not doing this?
+- **Technical design**: Data model, state, APIs, performance, migrations
+- **User experience**: Error states, loading, edge cases, accessibility
+- **Integration**: What else does this touch? Security? Observability?
+- **Tradeoffs**: What are you NOT building? What debt are you accepting?
+- **Risks**: What assumptions could be wrong? What would make this a failure?
+
+## Interview Flow
+
+1. Start with 2-4 questions per round via `AskUserQuestion`.
+2. Synthesize answers and follow up on gaps or ambiguities.
+3. Periodically summarize to confirm understanding.
+4. When sufficiently complete, confirm with the user and write the spec.
+
+## Output
+
+Write the spec to `docs/specs/<feature-name>.md` (or ask user for preferred path). Include whatever sections are relevant — don't force a rigid template.
+
+## Invocation
+
+```
+/spec-interview [topic]
+```