chore: upgrade pi dependencies from @mariozechner 0.72.0 to @earendil-works 0.75.5

pi 0.75.5 renamed the npm namespace from @mariozechner/ to @earendil-works/.
Importing from the old namespace causes 'fetch failed' errors at startup.

Changes:
- index.ts: @mariozechner/pi-ai → @earendil-works/pi-ai
- index.ts: @mariozechner/pi-coding-agent → @earendil-works/pi-coding-agent
- package.json: bump deps from 0.72.0 to 0.75.5
- package-lock.json: regenerated with new packages (242 deps)
- tsc --noEmit: zero errors