docs: start milestone v1.1 Foundations — Organizations + Passkeys

Update PROJECT.md with Current Milestone v1.1 section and Active
requirements list. Reset STATE.md for new milestone. Remove consumed
MILESTONE-CONTEXT.md. Clear 12 v1.0 phase directories from
.planning/phases/ (contents remain in git history; milestone-level
v1.0 docs preserved in .planning/milestones/). 999.x backlog phases
left in place.

Next: spawn 4 parallel research agents (STACK, FEATURES, ARCHITECTURE,
PITFALLS) covering multi-tenancy org patterns, passkey UX, invite flow
failure modes, and WebAuthn/MT CVEs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: szTheory