refactor: migrate commands to user-invocable skills

Claude Code has unified commands into skills with the user-invocable
frontmatter field. This migration:

- Converts 20 commands to skills with user-invocable: true
- Consolidates docs into single writing-capabilities.md
- Rewrites capability-writing skill for unified model
- Updates CLAUDE.md, Makefile, and other references
- Removes commands/ directory

Skills now have two types:
- user-invocable: true - workflows users trigger with /name
- user-invocable: false - background knowledge auto-loaded

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -18,8 +18,7 @@ make install
 | `manifesto.md` | Organization vision, personas, beliefs, principles |
 | `software-architecture.md` | Architectural patterns (human docs, mirrored in skill) |
 | `learnings/` | Historical record and governance |
-| `commands/` | AI workflow entry points (/work-issue, /manifesto, etc.) |
-| `skills/` | Tool and practice knowledge |
+| `skills/` | AI workflows and knowledge modules |
 | `agents/` | Focused subtask handlers |
 | `settings.json` | Claude Code configuration |
 | `Makefile` | Install symlinks to ~/.claude/ |
@@ -31,29 +30,28 @@ architecture/
 ├── manifesto.md              # Organization vision and beliefs
 ├── software-architecture.md  # Patterns linked to beliefs (DDD, ES)
 ├── learnings/                # Captured learnings and governance
-├── commands/                 # Slash commands (/work-issue, /dashboard)
-├── skills/         # Knowledge modules (auto-triggered)
-├── agents/         # Focused subtask handlers (isolated context)
-├── scripts/        # Hook scripts (pre-commit, token loading)
-├── settings.json   # Claude Code settings
-└── Makefile        # Install/uninstall symlinks
+├── skills/                   # User-invocable (/work-issue) and background skills
+├── agents/                   # Focused subtask handlers (isolated context)
+├── scripts/                  # Hook scripts (pre-commit, token loading)
+├── settings.json             # Claude Code settings
+└── Makefile                  # Install/uninstall symlinks
 ```
 
 All files symlink to `~/.claude/` via `make install`.
 
 ## Two Levels of Vision
 
-| Level | Document | Command | Purpose |
-|-------|----------|---------|---------|
+| Level | Document | Skill | Purpose |
+|-------|----------|-------|---------|
 | Organization | `manifesto.md` | `/manifesto` | Who we are, shared personas, beliefs |
 | Product | `vision.md` | `/vision` | Product-specific direction and goals |
 
 See the manifesto for our identity, personas, and beliefs about AI-augmented development.
 
-## Available Commands
+## Available Skills
 
-| Command | Description |
-|---------|-------------|
+| Skill | Description |
+|-------|-------------|
 | `/manifesto` | View/manage organization manifesto |
 | `/vision` | View/manage product vision and milestones |
 | `/work-issue <n>` | Fetch issue, create branch, implement, create PR |
@@ -79,28 +77,28 @@ tea logins add --name flowmade --url https://git.flowmade.one --token <your-toke
 ## Architecture Components
 
 ### Skills
-Knowledge modules that teach Claude how to do something.
 
+Skills come in two types:
+
+**User-invocable** (`user-invocable: true`): Workflows users trigger with `/skill-name`
+- **Purpose**: Orchestrate workflows with user interaction
+- **Location**: `skills/<name>/SKILL.md`
+- **Usage**: User types `/dashboard`, `/work-issue 42`, etc.
+
+**Background** (`user-invocable: false`): Knowledge auto-loaded when needed
 - **Purpose**: Encode best practices and tool knowledge
 - **Location**: `skills/<name>/SKILL.md`
-- **Usage**: Referenced by commands via `@~/.claude/skills/xxx/SKILL.md`
-
-### Commands
-User-facing entry points invoked with `/command-name`.
-
-- **Purpose**: Orchestrate workflows with user interaction
-- **Location**: `commands/<name>.md`
-- **Usage**: User types `/dashboard`, `/work-issue 42`, etc.
+- **Usage**: Referenced by other skills via `@~/.claude/skills/xxx/SKILL.md`
 
 ### Agents
 Focused units that handle specific subtasks in isolated context.
 
 - **Purpose**: Complex subtasks that benefit from isolation
-- **Location**: `agents/<name>/agent.md`
+- **Location**: `agents/<name>/AGENT.md`
 - **Usage**: Spawned via Task tool, return results to caller
 
 ### Learnings
-Captured insights from work, encoded into skills/commands/agents.
+Captured insights from work, encoded into skills/agents.
 
 - **Purpose**: Historical record + governance + continuous improvement
 - **Location**: `learnings/YYYY-MM-DD-title.md`