feat: scaffold us-cpa skill

skills/us-cpa/SKILL.md

@@ -0,0 +1,52 @@
+---
+name: us-cpa
+description: Use when answering U.S. federal individual tax questions, preparing a federal Form 1040 return package, or reviewing a draft/completed federal individual return.
+---
+
+# US CPA
+
+`us-cpa` is a Python-first federal individual tax workflow skill. The CLI is the canonical engine. Use the skill to classify the request, gather missing inputs, and invoke the CLI.
+
+## Modes
+
+- `question`
+  - one-off federal tax question
+  - case folder optional
+- `prepare`
+  - new or existing return-preparation case
+  - case folder required
+- `review`
+  - new or existing return-review case
+  - case folder required
+
+## Agent Workflow
+
+1. Determine whether the request is:
+   - question-only
+   - a new preparation/review case
+   - work on an existing case
+2. If the request is `prepare` or `review` and no case folder is supplied:
+   - ask whether to create a new case
+   - ask where to store it
+3. Use the bundled CLI:
+
+```bash
+skills/us-cpa/scripts/us-cpa question --question "What is the standard deduction?" --tax-year 2025
+skills/us-cpa/scripts/us-cpa prepare --tax-year 2025 --case-dir ~/tax-cases/2025-jane-doe
+skills/us-cpa/scripts/us-cpa review --tax-year 2025 --case-dir ~/tax-cases/2025-jane-doe
+```
+
+## Rules
+
+- federal individual returns only in v1
+- IRS materials first; escalate to primary law only when needed
+- stop on conflicting facts and ask the user to resolve the issue before continuing
+- official IRS PDFs are the target compiled-form artifacts
+- overlay-rendered forms must be flagged for human review
+
+## Output
+
+- JSON by default
+- markdown output available with `--format markdown`
+
+For operator details, limitations, and the planned case structure, see `docs/us-cpa.md`.