v0.6.45 — `reframe compose` — emit a composed SceneIR (overlay → IR), for live overlay preview

Added

reframe compose — emit a composed SceneIR (overlay → IR), for live overlay preview

• New verb reframe compose <scene.ts|.json> --overlay <doc>... [-o out.json] [--json] —
  composes overlay(s) onto a base and emits the composed SceneIR (no render). This is the
  IR half of the core composeScene (verify-overlay is its report half). stdout stays a
  bare SceneIR (pipe straight into player/frame); the applied/orphan report goes to stderr.
  Non-gating — orphans are reported but the partial IR is still emitted. Base may be a .ts
  source or a .json IR (composition is a post-compile IR→IR transform). Unblocks a live editor:
  manifest --json → build an OverlayDoc → compose → player, no mp4.
• --overlay on frame and player — compose-then-preview in one step (mirrors
  render --overlay): player scene.ts --overlay edits.json builds an instant interactive HTML
  with the edit applied; frame scene.ts --overlay edits.json renders a single PNG.
• compile --overlay now errors with a pointer instead of silently ignoring the flag
  (a footgun fix): compile is source→IR only; composition is a separate transform.
• Shared applyOverlays helper (packages/render-cli/src/overlay.ts) behind
  render/compose/frame/player, so they all compose + report identically. Closes #76.