feat(scene): animated zab-transition (mount fade/scale + leaf declaration); playout reloads browser to replay

[ClodoCapeo]

Stacked on #96 (forge/pulsar-m10-smooth-fade-playout). Makes the M10
transition VISIBLY animated, white+logo, and self-delivering the Blue rule
leaf. Refs #79.

Three coupled fixes

1. zab-transition.lsml.json — animate + declare the leaf

• animate directive on the logo (LSMLAnimateDirective: a single
  transition — transition{duration:550ms, easing:ease-out} + opacity +
  transform.scale). Authored mount fade/scale-in, no keyframes-compiler, no
  multi-step. Verified it compiles strict through @lumencast/compiler
  (Prism's vendored copy) to per-prop transitions (opacity/scale tween,
  duration_ms=550 → runtime 0.55s, ease cubic-out); the bundle
  round-trips byte-stable.
• Leaf declaration: operator_inputs declares
  __inputs.blue.m10-scene-control.scene_control (calque on
  m10-orion-scene.lsml.json), so Orion's sceneAcceptsPath (F2) fans the
  Blue delta out while this white+logo scene is active — no silent-drop, no
  magenta wipe-cover workaround. The render root stays white+logo: no
  keyframes block, no wipe-cover render element (leaf declared, not lowered
  to a cover).

2. Playout — replays the animation at each transition

• The local render page now plays the authored mount animation as CSS
  @keyframes keyed to page load (opacity 0→1, scale 0.85→1, the directive's
  duration/easing).
• Before each cut, the playout re-mounts the transition browser_source
  (re-SetCaptureSource with a cache-busted _replay= URL → a fresh CEF page
  load → the mount animation replays). obs-browser's same-URL Update()
  early-return would otherwise skip the reload, so the URL must differ.

3. Anti-faux-positif — prove the animation is VISIBLE

• Capture a sequence of frames (~8 @ ~80ms) across the mount window and
  prove a RAMP (prove_mount_ramp): the logo footprint grows from ~0 to
  its settled peak, with an intermediate frame neither blank nor already-
  settled. If every frame is identical/settled → NOT VISIBLE, said
  franchement (never declared "animated"); --allow-blank degrades to
  INCONCLUSIVE on a headless box. Keeps the settled white+logo MID + A + B +
  the Blue-rule target. C-SEC, --no-broadcast/--broadcast kept.

Known limitation (authoring info, not a defect)

In vanilla Solar today, the animate directive lowers to per-prop transition
timing only, and the runtime primitives (Image/Frame) set framer
animate without initial — so a static-prop animate does not itself
mount-play. The VISIBLE mount animation is produced by the browser_source
remount (a fresh page load replays the page's mount animation). The
real-Solar render at the antenna replays on reload the same way. Flagged for the
authoring session.

Tested

• @lumencast/compiler strict compile of the animate directive + the leaf
  declaration (✅, no warnings).
• pytest scripts/test_zab_transition.py — 24 tests (inverted static
  invariants → animate+leaf, + animate_mount_params, prove_mount_ramp
  ramp/settled/blank/too-few, _bust_url). Full CI offline set
  (test_m10_setup.py + test_probe_m10_real_orion.py + test_zab_transition.py
  • contracts/scene_control/) → 103 passed.
• ruff check clean on the changed Python.
• The visible animation (the ramp on a real CEF) is the Keeper run — the
  capture-sequence + ramp proof are wired to PROVE it; on a headless box it
  degrades to INCONCLUSIVE rather than a false "animated".

No test artefacts pushed (frames/VOD/pages live under gitignored build/).

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