feat: v0.1 scaffold command, examples, CI, release workflow

[lucasnevespereira]

Summary

Closes the remaining v0.1 roadmap items so users can install, scaffold, and build.

Changes

• inkssg new [path] — scaffolds pages/index/content.md + ink.yaml. Refuses if pages/ already exists.
• examples/minimal — one page, default theme.
• examples/multi-page — three pages sharing one theme.
• examples/library — standalone main.go calling inkssg.Build() via a replace directive.
• .github/workflows/ci.yml — vet + build + run each example on every push (catches embed/template breaks go build misses).
• .github/workflows/release.yml — on v* tags, builds linux/darwin × amd64/arm64 binaries and attaches them to a GitHub release with auto-generated notes.
• version switched from const to var so -ldflags -X main.version=... injects the tag at release build time.
• Fix: page.Theme = page.Theme self-assignment (was failing go vet).

Test plan

• go vet ./... clean
• go build ./... clean
• inkssg new /tmp/site && inkssg build /tmp/site produces public/index.html
• Each example builds locally
• Ldflag injection verified: go run -ldflags "-X main.version=v0.1.0-test" ./cmd/inkssg version prints inkssg v0.1.0-test
• CI passes on push
• Tag v0.1.0 produces a release with 4 binaries (validate after merge)