feat: migrate CLAUDE.md content to OpenSpec specs and initialize workflow

Move project description and tech stack research from CLAUDE.md into
openspec/specs/project/ and openspec/specs/stack/. Slim CLAUDE.md to a
pointer file. Populate config.yaml with project context. Add OpenSpec
CLI skills and commands.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openspec/changes/archive/2026-04-03-migrate-claude-md-to-openspec/design.md

@@ -0,0 +1,33 @@
+## Context
+
+CLAUDE.md is a monolithic file containing project identity, tech stack research, and stale GSD workflow sections. OpenSpec is now initialized and provides a structured home for this content as specs.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Move project description and constraints into `openspec/specs/project/spec.md`
+- Move technology stack research into `openspec/specs/stack/spec.md`
+- Populate `openspec/config.yaml` context so AI agents get project context when creating artifacts
+- Reduce CLAUDE.md to a slim file that points to OpenSpec for project knowledge
+
+**Non-Goals:**
+- Rewriting or editing the migrated content (faithful move, not a rewrite)
+- Creating conventions or architecture specs (those are still empty placeholders)
+- Changing any application code
+
+## Decisions
+
+### Decision 1: Spec file format
+
+The main specs in `openspec/specs/` will use a prose/reference format (not the WHEN/THEN delta format). The delta specs in the change use WHEN/THEN for requirements tracking, but the actual spec content is the migrated prose — tables, lists, and all.
+
+### Decision 2: CLAUDE.md post-migration content
+
+CLAUDE.md will retain only:
+- A one-line project summary
+- A pointer to `openspec/specs/` for project knowledge
+- Any workflow instructions specific to Claude Code (not project specs)
+
+### Decision 3: config.yaml context
+
+The `context` field in `openspec/config.yaml` will get a brief project summary and tech stack headline, so artifact generation has baseline context without reading full specs.