are.na-annual: publish pitch page at /are.na-annual

Moves the proposal page out of gigs/ and into system/public/ so it
resolves as a real route on aesthetic.computer. Contents unchanged
from the vibes draft: ~170-word pitch, thesis, three registers, and
all 68 channel blocks grouped by section with per-block rationale.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>