deps: drop flutter_svg in favor of PNG agent logos (shrink blast radius)

[leduckhc]

Summary

flutter_svg is used for a single purpose: rendering the 3 static agent logos (pi, codex, claude) at a fixed 40×40 on the home screen. It drags in a codec subtree:

flutter_svg → vector_graphics + vector_graphics_codec + vector_graphics_compiler

Since the logos are static and fixed-size, pre-rendering them as PNG (@2x/@3x) lets us drop flutter_svg and its ~3-package subtree, reducing the dependency blast radius (159 packages today; 20 direct).

Confirmed non-usage (safe to drop)

Audited during the CI-speedup work — flutter_svg is not used for anything else:

• Splash screen → flutter_native_splash uses a PNG (assets/makit-splash-mark.png), baked into native launch screens at build time. No runtime SVG.
• Animated brand mark (MakitClapMark "Clap loop") → pure CustomPainter + AnimationController. No SVG.
• No animation packages (lottie/rive) in the tree.
• Only consumer: app/lib/ui/home/home_screen.dart (SvgPicture.asset, logos map at ~L435).

Work

• Export assets/agents/{pi,codex,claude}.svg → PNG at @1x/@2x/@3x (40px base) into assets/agents/.
• Replace SvgPicture.asset(asset, ...) with Image.asset(asset, ...) in home_screen.dart; update the pi/codex/claude asset paths from .svg → .png.
• Add the @2x/@3x variants to pubspec.yaml assets (or rely on Flutter's resolution-aware asset resolution).
• Remove flutter_svg from pubspec.yaml; flutter pub get; verify vector_graphics* leave pubspec.lock.
• flutter analyze --fatal-infos clean; visually verify logos on the home screen (light + dark).

Tradeoff / non-goal

• Lose vector scalability for the logos — acceptable since they render at a fixed 40×40.
• http stays in the tree (also pulled by timezone via flutter_local_notifications), so this does not remove http.
• Modest win (~4 packages); flutter_svg is flutter.dev-published and low-risk, so this is hygiene, not urgent.

Context: raised while auditing deps during the CI-speedup PR (#22). Deferred out of that PR to keep it focused.