feat(coding-agent): add two-line footer example

[stevenahhh]

Part of #467

Summary

• add a public-API-only responsive two-line footer extension example
• head-elide long paths before dropping session metadata, preserving identifying path tails and the right-aligned model
• preserve host-provided built-in anchor indicators under the same condition as the default footer
• keep the built-in agent-context counter with left-side metrics while reserving other extension statuses at the right edge
• use the default footer's bullet separator instead of pipe separators
• sanitize terminal labels and preserve CJK-aware width handling

Verification

• npm run check
• npm test --workspace=@code-yeongyu/senpi -- test/examples/two-line-footer.test.ts — 17/17 passed
• fresh installed-Senpi PTY QA at 120 columns with short and long path states
• long-path capture remained two lines, retained session metadata, and ended both model and quota status at xterm cell 120
• independent TUI evidence review — PASS

Baseline note

The full Windows workspace suite still hits unchanged platform-specific failures/hangs in script path-regex and Ollama grep tests; the focused suite and all repository checks pass.