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/specs/project/spec.md

@@ -0,0 +1,24 @@
+## ADDED Requirements
+
+### Requirement: Project identity
+
+The project spec SHALL contain the project name, a description paragraph, and a core value statement that communicates the project's dual purpose: working AI chat interface and Blazor learning journey.
+
+#### Scenario: Project description present
+
+- **WHEN** an AI agent or developer reads the project spec
+- **THEN** they find the project name ("Chat Agent WebApp"), a description of what the app does, and the core value statement
+
+### Requirement: Project constraints
+
+The project spec SHALL enumerate all non-negotiable constraints that govern technical decisions across the project.
+
+#### Scenario: Constraints enumerated
+
+- **WHEN** a decision is made about technology, architecture, or approach
+- **THEN** the project spec provides the authoritative list of constraints to check against:
+  - Tech stack: .NET / C# / Blazor WebAssembly
+  - LLM provider: OpenAI GPT API
+  - Storage: JSON files on local disk
+  - Architecture: WASM client + backend API (API key stays server-side)
+  - Code style: Every Blazor concept introduced MUST have inline comments explaining what it does and why