examples: add statusline script with context window and rate limit bars

[DGDrago]

Summary

• Adds examples/statusline/statusline-command.sh — a Bash/Node.js statusline showing model name, current directory, color-coded context window bar, session cost, clock, and 5-hour rate limit bar
• Adds examples/statusline/README.md with install instructions including Windows (Git Bash) path format
• Works on macOS, Linux, and Windows (Git Bash / WSL); requires only Node.js

What it looks like

Sonnet 4.6  D:\myproject >  ████████░░ 42k left (21%)  $0.2817  21:45  Resets in 2 hr 14 min – ███░░░░░░░ 30% used

Color coding:

• Context bar: green (>50% left) → yellow (>25%) → red
• Rate limit bar: blue (<50% used) → yellow (<80%) → red

Test plan

• Copy script, chmod +x, set statusLineCommand, verify it renders in terminal
• Test on macOS/Linux with ~/.claude/ path
• Test on Windows with /C/Users/<you>/.claude/ path (Git Bash)