v0.15.0 — Composable embedding

The v0.15.0 milestone delivers the cluster of runes and infrastructure that makes refrakt's "embed anything inline" story real: a body-only drawer rune with xref-as-trigger (SPEC-060), an expand rune that inlines registered entities (SPEC-066), a snippet rune that embeds project files as syntax-highlighted code (SPEC-062), and the supporting plumbing that ties them together: $page.*/$file.* page variables (SPEC-061), generic file roots for namespaced file resolution (SPEC-063), unconditional plan-entity registration (SPEC-064), and configurable xref resolution with patterns and decoupled entity/URL lookup (SPEC-065).

Once these land, the same .md file can render as its own canonical page, embed inline via expand, open as a drawer panel from a sentence in prose, or quote-link via xref — all from one source. That's the unique authoring story behind the future "see it in action" introduction article (SPEC-067, deferred).