fix(lint): ignore entrance opacity in scene exit rule

[miguel-heygen]

What

• distinguish actual opacity-zero exit tweens from the first vars object of entrance-only fromTo calls
• add regression coverage for a final scene that enters from opacity zero and never exits

Why

scene_layer_missing_visibility_kill matched any nearby opacity: 0. A final scene authored with fromTo(scene, {opacity:0}, {opacity:1}) was incorrectly treated as exiting and told to hide itself at the end of the video.

How

The rule now recognizes opacity-zero values only in .to() destination vars or the second destination-vars object of .fromTo(). Entrance-only from-vars no longer trigger the hard-kill requirement.

Test plan

• bun run --cwd packages/lint test --run src/rules/gsap.test.ts (83/83)
• pre-commit lint, format, fallow, and typecheck hooks