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

[Keinberger]

Overview

This updates the project-template skills for the current Miden v0.16 code line on main. PR #61 already migrated the code and non-skill docs; this PR is now based directly on main and contains only .claude/skills/** changes.

Changes

• Rebases the skills branch onto main at fbe051d so GitHub shows only the seven skill-file deltas.
• Aligns the shared Rust SDK skills with the current project-template manifests, nightly-2026-09-01, midenup / cargo-miden build flow, and lockfile-resolved v0.16 host crates.
• Incorporates the relevant chore(skills): migrate agent-tools skills to Miden v0.16 agent-tools#17 review feedback for the shared skill files: Rust 1.99 toolchain guidance, append-based output-note attachment APIs, and embedded WIT plus package-cache dependency resolution.
• Preserves and migrates the project-template Miden Day skill coverage for cross-component notes, miden-client CLI usage, .masp note construction, and MockChain note interactions.
• Keeps the project-only miden-client-cli skill aligned with midenup component invocation while documenting direct miden-client-cli 0.16.0-rc.2 installation as the exact Cargo.lock parity path.

Verification

• gh pr diff 64 --repo 0xMiden/project-template --name-only lists only the seven .claude/skills/**/SKILL.md files.
• git diff --name-only origin/main...HEAD lists only the same seven skill files.
• git diff --check origin/main..HEAD produced no output.
• Stale-content scan for old rc/toolchain/WIT/attachment/repo-name phrases produced no output.
• Frontmatter for all seven touched skill files still contains name and description metadata.

Closes #63