feat: initial commit - opencode spec-driven development boilerplate

Converted from Claude Code boilerplate to opencode:
- CLAUDE.md -> AGENTS.md (opencode instructions)
- .claude/settings.json -> opencode.json (permissions schema)
- .claude/agents/ -> .opencode/agent/ (subagents with mode: subagent)
- .claude/commands/ -> .opencode/command/ (slash commands with )
- .claude/skills/ -> .opencode/skills/ (7 skills, removed allowed-tools)
- DevContainer updated to install opencode
- All .claude/ paths and Claude Code references updated

.opencode/skills/glossary-creation/SKILL.md

@@ -0,0 +1,55 @@
+---
+name: glossary-creation
+description: Detailed guide and template for creating a glossary. Use only when creating a glossary.
+---
+
+# Glossary Creation Skill
+
+This skill is a detailed guide for systematically defining project-specific terms and technical terms.
+
+## Prerequisites
+
+Before starting to create a glossary, confirm the following:
+
+### Recommended Documents
+
+1. **docs/product-requirements.md** (PRD)
+2. **docs/functional-design.md** (Functional Design Document)
+3. **docs/architecture.md** (Architecture Design Document)
+4. **docs/repository-structure.md** (Repository Structure)
+5. **docs/development-guidelines.md** (Development Guidelines)
+
+The glossary defines the terms used across all documents in a unified way.
+Extract terms from each document and organize them systematically.
+
+## Priority of Existing Documents
+
+**Important**: If an existing glossary is present at `docs/glossary.md`,
+follow the priority order below:
+
+1. **Existing glossary (`docs/glossary.md`)** - Highest priority
+   - Contains project-specific term definitions
+   - Takes precedence over this skill's guide
+
+2. **This skill's guide** - Reference material
+   - Generic templates and examples
+   - Use when no existing glossary exists, or as a supplement
+
+**When creating new**: Refer to this skill's template and guide
+**When updating**: Update while maintaining the structure and content of the existing glossary
+
+## Output Destination
+
+Save the created glossary to the following location:
+
+```
+docs/glossary.md
+```
+
+## Template Reference
+
+When creating a glossary, use the following template: ./template.md
+
+## Detailed Guide
+
+For a more detailed creation guide, refer to the following file: ./guide.md