perf: optimize cursor loading by deferring heavy operations

[kanetronv2]

Fixes #86

Optimizes cursor loading performance by deferring heavy operations that were blocking the main thread during terminal initialization.

Changes:

• Move ASCII art and file preloading after terminal initialization
• Process images in batches with delays to prevent blocking main thread
• Load remote files asynchronously with staggered timing
• Add lazy loading fallback for ASCII art on-demand

This allows the terminal cursor to become responsive immediately while background assets load progressively.

Generated with Claude Code

[ledwards]

The diagnosis was right, and the fix landed — just via a different route.

#109 ("Improve terminal startup interactivity") restructured the same startup path: preloadASCIIArt() and preloadFiles() now run inside window.scheduleIdleTask(...) from js/bootstrap.js, so they yield to the browser instead of blocking first paint. That uses requestIdleCallback rather than a chain of staggered setTimeouts, which gets the same "don't block interactivity" result without guessing at delays.

Reported improvements from that work: homepage prompt visible 1941ms → 70ms, first command rendered 2076ms → 223ms.

The PR conflicts against the rewritten files and there's nothing left in it to port, but this was the correct read of the problem.