M4.12: docs: ROADMAP, parity, web, preferences and agents brought up to date after M3 and M4

- parity: the status note covers the M3.9–M4.12 passes (feature counts unchanged: they fixed
  behaviour inside features already counted done) and the GPU effect count matches EFF-5 (280);
  the Layers, Compositions, Interface, Project and Preview rows name what is left and what
  landed; landed items in "Highest-value gaps" are struck through with where they landed, the
  gaps the passes left are items 16–18, and the closing paragraph no longer says 69 menu entries
  are disabled.
- ROADMAP: what is left includes the preview gaps.
- web: a restored session with unsaved changes stays modified and asks before closing.
- preferences: Adaptive Resolution Limit applies while dragging, not to playing previews.
- agents: nested comp settings and New Comp from Selection for several items.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

ROADMAP.md

@@ -33,6 +33,7 @@ Measured feature by feature in [docs/parity.md](docs/parity.md) (4 October 2026)
 - **≈ 8.5 agent-hours of work remain**: about **2–3 hours of wall-clock time** with five Claude
   Opus 5.5 agents in parallel, ≈ 1 hour without learned models for Roto Brush and face tracking.
 - What is left: GPU kernels for the remaining visual effects, and learned-model quality for Roto
-  Brush and face tracking.
+  Brush and face tracking; in previews, motion blur of collapsed precomps and of animated layer
+  content, and content-keyed RAM preview frames ([parity.md](docs/parity.md#highest-value-gaps-in-order)).
 
 Come tell us what matters most to you on [Discord](https://discord.gg/artcraft).