feat: mcp+CLI agent references

[Rodriguespn]

What kind of change does this PR introduce?

Adds MCP and CLI tooling references to the existing Supabase skill.

What is the current behavior?

The Supabase skill has references for database concepts (RLS, schema design, migrations, performance) but lacks guidance on tooling. Agents don't know:

• How to connect to the Supabase MCP server
• When to use MCP tools vs CLI commands
• How CLI commands work (unlike MCP tools, CLI has no self-describing schema)
• How to combine MCP and CLI for optimal workflows

What is the new behavior?

The skill now provides comprehensive tooling guidance:

MCP Setup - Configuration references for connecting to local, hosted, and self-hosted MCP servers, including security considerations and available feature groups.

CLI Command References - LLM-friendly documentation for all major CLI commands grouped by category (project, database, migrations, functions, secrets, generation). Each group includes command syntax, flags, and comparison with equivalent MCP tools.

Combined Workflows - Patterns showing how MCP and CLI work together. For example, local development uses CLI for stack management, MCP for rapid iteration (no migration files cluttering history), and CLI to capture the final state.

Tool Selection Framework - Clear guidance on when to prefer MCP (remote operations, no setup needed) vs CLI (local-only operations, file generation).

Decisions

Key architectural and content decisions made during development:

1. MCP first, CLI fallback: Agents should prefer MCP tools when connected because they require no link setup. CLI is used for local-only operations (start/stop/reset) and as fallback when MCP is unavailable.

2. Grouped CLI files instead of individual: Organized 18+ CLI commands into 6 category files (project, database, migrations, functions, secrets, generation) rather than one file per command. Reduces context overhead while maintaining discoverability.

3. CLI needs descriptions, MCP doesn't: MCP tools are self-describing via the server connection - agents receive tool schemas automatically. CLI commands have no such mechanism, so they need LLM-friendly documentation in the skill.

4. Workflow-focused combined references: Rather than documenting MCP and CLI separately, created workflow patterns showing them working together (local dev, migration creation, type generation, function development).

Additional context

Sources consulted:

• Supabase CLI documentation via mcp__supabase__search_docs
• Supabase MCP server documentation
• Existing kiro-powers patterns for CLI + MCP workflows

Includes a decision-guide.md with instructions on which command to choose depending on the workflow and a common-pitfall file with common mistakes that agents make with Supabase CLI (Thanks @jorgoose for the suggestion - #26)