chore: initial project setup with agent guide

.agent/skills/gsd-validate-phase/SKILL.md

@@ -0,0 +1,26 @@
+---
+name: gsd-validate-phase
+description: Retroactively audit and fill Nyquist validation gaps for a completed phase
+---
+
+<objective>
+Audit Nyquist validation coverage for a completed phase. Three states:
+- (A) VALIDATION.md exists — audit and fill gaps
+- (B) No VALIDATION.md, SUMMARY.md exists — reconstruct from artifacts
+- (C) Phase not executed — exit with guidance
+
+Output: updated VALIDATION.md + generated test files.
+</objective>
+
+<execution_context>
+@.agent/get-shit-done/workflows/validate-phase.md
+</execution_context>
+
+<context>
+Phase: $ARGUMENTS — optional, defaults to last completed phase.
+</context>
+
+<process>
+Execute @.agent/get-shit-done/workflows/validate-phase.md.
+Preserve all workflow gates.
+</process>