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/functional-design/template.md

@@ -0,0 +1,262 @@
+# Functional Design Document
+
+## System Architecture Diagram
+
+```mermaid
+graph TB
+    User[User]
+    CLI[CLI Layer]
+    Service[Service Layer]
+    Data[Data Layer]
+
+    User --> CLI
+    CLI --> Service
+    Service --> Data
+```
+
+## Technology Stack
+
+| Category | Technology | Selection Rationale |
+|------|------|----------|
+| Language | [Language name] | [Rationale] |
+| Framework | [Name] | [Rationale] |
+| Database | [Name] | [Rationale] |
+| Tools | [Name] | [Rationale] |
+
+## Data Model Definition
+
+### Entity: [Entity Name]
+
+```typescript
+interface [EntityName] {
+  id: string;              // UUID
+  [field1]: [type];        // [description]
+  [field2]: [type];        // [description]
+  createdAt: Date;         // Creation timestamp
+  updatedAt: Date;         // Update timestamp
+}
+```
+
+**Constraints**:
+- [Constraint 1]
+- [Constraint 2]
+
+### ER Diagram
+
+```mermaid
+erDiagram
+    ENTITY1 ||--o{ ENTITY2 : has
+    ENTITY1 {
+        string id PK
+        string field1
+        datetime createdAt
+    }
+    ENTITY2 {
+        string id PK
+        string entity1Id FK
+        string field1
+    }
+```
+
+## Component Design
+
+### [Component 1]
+
+**Responsibilities**:
+- [Responsibility 1]
+- [Responsibility 2]
+
+**Interface**:
+```typescript
+class [ComponentName] {
+  [method1]([params]): [return];
+  [method2]([params]): [return];
+}
+```
+
+**Dependencies**:
+- [Dependency 1]
+- [Dependency 2]
+
+## Use Case Diagram
+
+### [Use Case 1]
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant CLI
+    participant Service
+    participant Data
+
+    User->>CLI: [action1]
+    CLI->>Service: [action2]
+    Service->>Data: [action3]
+    Data-->>Service: [response]
+    Service-->>CLI: [response]
+    CLI-->>User: [result]
+```
+
+**Flow Description**:
+1. [Step 1]
+2. [Step 2]
+3. [Step 3]
+
+## Screen Transition Diagram (if applicable)
+
+```mermaid
+stateDiagram-v2
+    [*] --> State1
+    State1 --> State2: [action]
+    State2 --> State3: [action]
+    State3 --> [*]
+```
+
+## API Design (if applicable)
+
+### [Endpoint 1]
+
+```
+POST /api/[resource]
+```
+
+**Request**:
+```json
+{
+  "[field]": "[value]"
+}
+```
+
+**Response**:
+```json
+{
+  "id": "uuid",
+  "[field]": "[value]"
+}
+```
+
+**Error Responses**:
+- 400 Bad Request: [Condition]
+- 404 Not Found: [Condition]
+- 500 Internal Server Error: [Condition]
+
+## Algorithm Design (if applicable)
+
+### [Algorithm Name]
+
+**Purpose**: [Description]
+
+**Calculation Logic**:
+
+#### Step 1: [Step Name]
+- [Detailed description]
+- Formula: `[formula]`
+- Score range: 0-100 points
+
+#### Step 2: [Step Name]
+- [Detailed description]
+- Formula: `[formula]`
+- Score range: 0-100 points
+
+#### Step 3: Total Score Calculation
+- Weighted average: `Total Score = (Step 1 × Weight 1) + (Step 2 × Weight 2)`
+- Weight allocation:
+  - Step 1: [%]
+  - Step 2: [%]
+
+#### Step 4: Classification
+- [Classification 1]: Score >= [threshold]
+- [Classification 2]: [threshold] <= Score < [threshold]
+- [Classification 3]: Score < [threshold]
+
+**Implementation Example**:
+```typescript
+function [algorithmName]([params]): [return] {
+  // Step 1
+  const score1 = [calculation];
+
+  // Step 2
+  const score2 = [calculation];
+
+  // Total score
+  const totalScore = (score1 * weight1) + (score2 * weight2);
+
+  // Classification
+  if (totalScore >= threshold1) return '[classification1]';
+  if (totalScore >= threshold2) return '[classification2]';
+  return '[classification3]';
+}
+```
+
+## UI Design (if applicable)
+
+### Table Display
+
+**Display Items**:
+| Item | Description | Format |
+|------|------|-------------|
+| [Item 1] | [Description] | [Format] |
+| [Item 2] | [Description] | [Format] |
+
+### Color Coding
+
+**Color Usage**:
+- [Color 1]: [Use] (e.g., green = completed)
+- [Color 2]: [Use] (e.g., yellow = in progress)
+- [Color 3]: [Use] (e.g., red = not started)
+
+### Interactive Mode (if applicable)
+
+**Operation Flow**:
+1. [Operation 1]
+2. [Operation 2]
+3. [Operation 3]
+
+## File Structure (if applicable)
+
+**Data Storage Format**:
+```
+[directory]/
+├── [file1].json    # [description]
+└── [file2].json    # [description]
+```
+
+**File Content Example**:
+```json
+{
+  "[field]": "[value]"
+}
+```
+
+## Performance Optimization
+
+- [Optimization 1]: [Description]
+- [Optimization 2]: [Description]
+
+## Security Considerations
+
+- [Consideration 1]: [Countermeasure]
+- [Consideration 2]: [Countermeasure]
+
+## Error Handling
+
+### Error Classification
+
+| Error Category | Handling | Display to User |
+|-----------|------|-----------------|
+| [Category 1] | [Handling details] | [Message] |
+| [Category 2] | [Handling details] | [Message] |
+
+## Testing Strategy
+
+### Unit Tests
+- [Target 1]
+- [Target 2]
+
+### Integration Tests
+- [Scenario 1]
+- [Scenario 2]
+
+### E2E Tests
+- [Scenario 1]
+- [Scenario 2]