Initialize project skeleton with CLI and documentation

Add initial project structure including:
- Go module with Cobra CLI dependency
- Root command and main entrypoint
- Basic documentation (README, AGENTS.md, architecture, decisions,
  development, roadmap)
- Configuration example and gitignore
- Tool version management with mise
- Comprehensive project rules and conventions

docs/decisions.md

@@ -0,0 +1,19 @@
+# Technical Decisions
+
+Record significant technical decisions as they are made. Use the format below.
+
+## Template
+
+```
+## YYYY-MM-DD: Title
+
+**Context**: Why this decision was needed.
+
+**Decision**: What was decided.
+
+**Consequences**: What this means for the project.
+```
+
+## Decisions
+
+*(None yet. Add entries as decisions are made.)*