chore: initialize repository with project docs and tooling

- Add persistent docs: PRD, functional design, architecture, repository structure, development guidelines, milestones

- Add brainstorming notes (docs/ideas/)

- Configure tooling: package.json, tsconfig, eslint, prettier, vitest

- Add opencode configuration (commands, skills, agents)

- Add .gitignore for node_modules, .env, data/, backups/, build outputs

AGENTS.md

@@ -0,0 +1,134 @@
+# Project Memory
+
+## Technology Stack
+
+- Development environment: devcontainer
+- Node.js v24.11.0
+- TypeScript 5.x
+- Package manager: npm
+
+## Basic Principles of Spec-Driven Development
+
+### Basic Flow
+
+1. **Document creation**: Define "what to build" in persistent documents (`docs/`)
+2. **Work planning**: Plan "what to do this time" in steering files (`.steering/`)
+3. **Implementation**: Implement according to tasklist.md and update progress as you go
+4. **Verification**: Testing and operation checks
+5. **Update**: Update documents as needed
+
+### Important Rules
+
+#### When Creating Documents
+
+**Create one file at a time, and always obtain the user's approval before moving on to the next.**
+
+When waiting for approval, communicate clearly:
+```
+"The creation of [document name] is complete. Please review the content.
+Once you approve, I will proceed to the next document."
+```
+
+#### Checks Before Implementation
+
+Before starting a new implementation, always check the following:
+
+1. Read AGENTS.md
+2. Read the related persistent documents (`docs/`)
+3. Search for existing similar implementations with Grep
+4. Understand existing patterns before starting implementation
+
+#### Steering File Management
+
+Create `.steering/[YYYYMMDD]-[task-name]/` for each piece of work:
+
+- `requirements.md`: The requirements for this work
+- `design.md`: The implementation approach
+- `tasklist.md`: A concrete task list
+
+Naming convention: `20250115-add-user-profile` format
+
+#### Steering File Management
+
+**Use the `steering` skill when planning work, implementing, and verifying.**
+
+- **When planning work**: Mode 1 (creating steering files) via the steering skill
+- **When implementing**: Mode 2 (implementation and tasklist.md update management) via the steering skill
+- **When verifying**: Mode 3 (retrospective) via the steering skill
+
+Detailed procedures and update-management rules are defined within the steering skill.
+
+## Directory Structure
+
+### Persistent Documents (`docs/`)
+
+Define "what to build" and "how to build it" for the entire application:
+
+#### Drafts and Ideas (`docs/ideas/`)
+- Outputs of brainstorming and ideation
+- Technical research notes
+- Free-form (minimal structure)
+- Automatically loaded when `/setup-project` is run
+
+#### Official Documents
+- **product-requirements.md** - Product requirements document
+- **functional-design.md** - Functional design document
+- **architecture.md** - Technical specification
+- **repository-structure.md** - Repository structure definition document
+- **development-guidelines.md** - Development guidelines
+- **glossary.md** - Ubiquitous language definitions
+
+### Work-Unit Documents (`.steering/`)
+
+Define "what to do this time" for a specific development task:
+
+- `requirements.md`: The requirements for this work
+- `design.md`: The design of the changes
+- `tasklist.md`: The task list
+
+### opencode Configuration (`.opencode/`)
+
+- `.opencode/agent/` - Subagent definitions (doc-reviewer, implementation-validator)
+- `.opencode/command/` - Slash commands (setup-project, add-feature, review-docs)
+- `.opencode/skills/` - Task-specific skills (prd-writing, functional-design, architecture-design, repository-structure, development-guidelines, glossary-creation, steering)
+
+## Development Process
+
+### Initial Setup
+
+1. Use this template
+2. Create persistent documents with `/setup-project` (interactively creating six)
+3. Implement features with `/add-feature [feature]`
+
+### Day-to-Day Usage
+
+**Basically, just make requests through normal conversation:**
+
+```bash
+# Editing documents
+> Please add a new feature to the PRD
+> Review the performance requirements in architecture.md
+> Add a new domain term to glossary.md
+
+# Adding features (use commands for the standard flow)
+> /add-feature edit user profile
+
+# Detailed review (when a detailed report is needed)
+> /review-docs docs/product-requirements.md
+```
+
+**Key point**: You do not need to be conscious of the details of spec-driven development. opencode will determine and load the appropriate skill.
+
+## Principles of Document Management
+
+### Persistent Documents (`docs/`)
+
+- Describe the fundamental design
+- Not updated frequently
+- The "north star" for the entire project
+
+### Work-Unit Documents (`.steering/`)
+
+- Specialized for a specific task
+- Created anew for each piece of work
+- Retained as history