chore[tool]: move skills to invocable paths

[devin-ai-integration]

What I did

Moved the repo’s skill docs into Devin-recognized skill paths so they can be surfaced as model-invocable skills by default:

• .agents/skills/vyper-compiler/SKILL.md for compiler internals, with existing topic docs beside it.
• .agents/skills/vyper-review-contributing/SKILL.md for PR review and contribution workflow.

How I did it

• Renamed the existing skills/ bundle into .agents/skills/vyper-compiler/.
• Renamed skills/contributing.md into its own .agents/skills/vyper-review-contributing/SKILL.md and added name/description frontmatter.
• Updated CLAUDE.md and intra-skill links for the new paths.
• Adjusted .gitignore so committed .agents/skills/** files are allowed while other .agents scratch files stay ignored.

How to verify it

• skill search /home/ubuntu/repos/vyper --keywords vyper
• Confirm both vyper-compiler and vyper-review-contributing appear.
• Confirm markdown links resolve from the new .agents/skills/ locations.

Commit message

move the repo skill docs into `.agents/skills` so Devin can surface
them as model-invocable skills in repository sessions. split the PR
review/contribution workflow into its own skill, and keep compiler
internals under a separate compiler-focused skill.

allow committed `.agents/skills` entries through `.gitignore`, while
leaving other `.agents` scratch files ignored.

Description for the changelog

N/A

Cute Animal Picture

Link to Devin session: https://app.devin.ai/sessions/e91eca192f7d421a9b9a41698d0d2c8f
Requested by: @charles-cooper

[devin-ai-integration]

🤖 Devin AI Engineer

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[github-actions]

Gas Changes

No changes detected.

Summary

• Total tests measured: 815
• Changed: 0
• Regressions (gas up): 0
• Improvements (gas down): 0
• New tests: 0
• Deleted tests: 0
• Newly failing: 0
• Newly passing: 0

[github-actions]

📊 Bytecode Size Changes (venom)

No changes detected.

Full bytecode sizes

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