Radically simplify statusline to 5 essential fields

[virtualian]

Problem

The current PAI statusline is multi-line, information-dense, and breaks when CC notification banners share the row (upstream issue anthropics/claude-code#24638). The complexity also makes it fragile across terminal widths.

Constraint

Max width: 19 characters. This is the actual rendering width available when CC notification banners are active. The statusline must never exceed 19 chars on any line.

Proposal

Stacked single-column layout, max 19 chars per line:

42% 15m
~/projects/pai
main

Fields (3 lines, all ≤19 chars):

1. Line 1: Context % (color-coded) + Session time
2. Line 2: PWD (abbreviated, truncated to 19 chars)
3. Line 3: Git branch (truncated to 19 chars)

Why

• Fits within 19-char CC panel width when notifications are active
• No width detection or responsive modes needed
• Faster execution (fewer git/system calls)
• All non-essential info removed
• Resilient to CC layout changes

Removes

• PAI version
• Location/weather section
• ENV section (CC version, skills/workflows/hooks counts)
• Memory section
• Learning section
• ANSI art separators and headers
• Responsive mode system (pico/nano/micro/mini/normal)

Acceptance Criteria

• No line exceeds 19 visible characters
• Context % color-coded by threshold
• PWD abbreviated (home → ~, truncated to 19 chars)
• Branch truncated to 19 chars
• Script executes in < 100ms