feat: add supermodel skill command for agent awareness prompt

[jonathanpopham]

What

supermodel skill prints a prompt that teaches agents how to use graph shard files.

$ supermodel skill >> CLAUDE.md
$ supermodel skill >> AGENTS.md

Why

Benchmark data shows agents need to be told about shard files. Without prompting, they ignore or filter them out. With prompting: 43% cost savings on complex tasks (Lance's 14-repo test), 68% faster on Medusa (our test).

The prompt

This repository has Supermodel graph shard files next to source files.

Files ending in .calls.* contain function call relationships (who calls what, with file and line number).
Files ending in .deps.* contain dependency relationships (imports and imported-by).
Files ending in .impact.* contain blast radius data (risk level, affected domains, direct/transitive dependents).

When navigating the codebase:
- Read .deps files to understand what a module depends on and what depends on it
- Read .calls files to trace call chains across files
- Read .impact files to assess the blast radius before making changes
- These files appear in grep/rg results alongside source code — use the data to navigate faster

1 file, 38 lines.

Closes #118

Summary by CodeRabbit

• New Features
  • Added a new skill command that provides comprehensive documentation about Supermodel graph shard files. When executed, the command displays information explaining the .calls.*, .deps.*, and .impact.* file types, their purpose and semantics, along with guidance on how to effectively navigate and use them throughout the repository.

[coderabbitai]

Caution

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Walkthrough

A new skill CLI subcommand was added that prints an informational prompt explaining Supermodel's shard files (.calls.*, .deps.*, .impact.*) and how agents should use them when navigating the codebase.

Changes

Cohort / File(s)	Summary
Skill Command cmd/skill.go	New Cobra subcommand that registers with rootCmd and outputs a predefined prompt about graph shard awareness for agents.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🧠 A skill command stands so proud,
Teaching agents, speaking loud,
"Read the .calls, .deps aloud!"
Shards revealed, no more shrouded,
Smarter queries, less cloud! ✨

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Quick breakdown for you: This change is super straightforward—it's basically just adding a new command to your CLI that prints out helpful instructions. Think of it like adding a cheat sheet command. When someone runs supermodel --skill, they get a formatted message explaining that those .calls, .deps, and .impact files are gold for understanding the code structure. The whole implementation is just defining what that message says and hooking it up to the CLI system (Cobra). No complex logic, no weird edge cases—just a helpful command that spits out text.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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_{Comment @coderabbitai help to get the list of available commands and usage tips.}