Add cinematic first-visit splash intro + route transitions; optimize …

[JacobDChamberlain]

…bone logo

Splash intro (new SplashIntro component):

• First-visit-only "lights down" curtain gated on sessionStorage; never replays on client-side route changes
• Skippable via click / tap / scroll / key; decode-gated so the logo never animates half-loaded, with a 1.5s fallback so a stalled decode can't strand a black screen
• Lightning double-strike that inverts the logo itself, mirroring the existing Header.css lightning effect
• Honors prefers-reduced-motion (quick fade, no lightning/grain/scale); fully opaque overlay dissolves to reveal the already-rendered site
• Reserve the scrollbar gutter (html { scrollbar-gutter: stable }) so the splash scroll-lock never reflows the page on classic-scrollbar browsers

Route transitions:

• AnimatedRoutes crossfades each page in on navigation (~280ms), disabled under prefers-reduced-motion

Logo optimization:

• Replace the 8.9MB Maldevera_logo-BONE_TEXTURE.png with a 212KB WebP (resized 5906px -> 1400px, visually identical at display size); update the splash and header references. Full-res master kept out of the bundle.

Includes SPLASH_RESEARCH.md documenting the research and acceptance criteria.