feat(claude-setup): derive skill version from release tag; port SKILL.md lazy-load guidance

[stepan-romankov]

What

• Drop the hand-maintained skill version. Replace the inline <!-- samurai-skill-v3 --> marker + const version = "3" with a version derived at install time from the module release via runtime/debug.ReadBuildInfo() (Main.Version). The marker written into installed SKILL.md becomes the release tag, e.g. <!-- samurai-skill-v0.9.0 -->; local builds fall back to dev.
• Fix a latent double-marker bug. main.go appended a marker to embedded content that already ended with one, so fresh installs wrote it twice. Removing the inline marker from the source SKILL.md leaves a single, runtime-generated marker.
• Port three generic SKILL.md improvements that had diverged in a downstream copy: a Good For / Bad For summary, a lazy-load resources heading, and per-file "read only when" guidance for api.md / pitfalls.md.

Why

Cutting a git tag/release is already done every time the skill changes, so a separate hand-synced skill version was redundant duplication (and drifted before — see commit 16ac1f7). Tying the marker to the release tag means creating the tag is the version bump; the installer auto-detects when a downstream copy is stale.

Trade-off

The marker now changes on every release, so a downstream re-install rewrites the skill files even when the skill content was unchanged. Acceptable: re-installing is an intentional manual action, and it skips when the installed marker already matches the running binary's release.

Verification

• go build ./cmd/claude-setup, go vet, go test ./... — all pass.
• Scratch install: writes a single marker; second run reports "already up to date"; installed file = source body + one appended marker line.

🤖 Generated with Claude Code