Support queued prompt templates and Agent Skills

[tmustier]

Summary

• expand discovered prompt templates and Agent Skills when their queued row reaches delivery
• support Pi’s /skill:name form plus non-shadowing short aliases such as /bro
• preserve images, FIFO ordering and editable raw rows
• restore and pause a full batch if expansion fails
• reject extension commands that Pi cannot invoke through its public extension API

Testing

• npm run ci (53 tests)
• interactive smoke test with Pi 0.84.1: /do-less … remained raw while queued and expanded on delivery; /bro delivered as the bro skill
• npm pack --dry-run --json confirms queued-input.ts is packaged