chore(skills): migrate project template skills to Miden v0.16

## Background

PR #61 migrates the project template code to Miden v0.16 and intentionally leaves `.claude/skills/` unchanged. The shared v0.16 skill migration is being developed in 0xMiden/agent-tools#17.

## Problem

The project template still ships seven v0.15-era skill files, so generated projects can receive guidance that does not match the v0.16 code and dependencies.

## Proposed Solution

Port the six matching v0.16 skills from 0xMiden/agent-tools#17 and migrate the project-only `miden-client-cli` skill separately. Deliver the changes in a draft PR stacked on #61 so the code migration remains reviewable on its own.

Any thoughts on this are highly appreciated!

The skills to migrate are in the `.claude/skills/` directory. Compare the existing v0.15 skill files with the v0.16 versions from the linked PR in the 0xMiden/agent-tools repository. Update each skill file to match the v0.16 format and logic, ensuring they align with the project template's migrated code. Test by generating a project and verifying the skills provide correct guidance.

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