docs: establish domain vocabulary and identity scenarios (#5) - #6

Summary

Medora now has a shared domain vocabulary and a stack-neutral relationship model grounded in the confirmed product foundation. The first modeling round establishes Staff Account versus Practice Membership, shared Contact Points and requests that survive reservation expiry.

GLOSSARY.md            resolved definitions only
docs/domain-model.md   accepted relationships and open scenarios
.planning/decisions/   exact replies, interpretation and dependencies

Refs #5. Domain modeling remains active. The next questions concern active reservation limits, appointment continuity during rescheduling and receptionist coverage. These remain proposals; detailed booking and access follow-ups are still in progress. No stack, schema or application implementation is selected.

Evidence

• Before: product scope existed without a canonical glossary or domain relationship model.
• After: vocabulary and accepted relationships have linked decision records; the joint reply is preserved verbatim, separately from its interpretation. Unanswered scenarios remain explicit. Repository/link, planning metadata and staged whitespace checks pass.

Merge Danger

Door: two-way

Documentation and terminology only; the modeling session remains open and this PR stays draft.

Blast Radius: planning