docs: add the data family (orm + schema + adapters) [#72, HOLD until publish + #66]

[suleimansh]

Closes #72 (when merged). Part of the data-layer graduation epic #64.

Sweeps every package-list surface to include the four new packages now on main (orm, schema, orm-memory, orm-drizzle):

• README.md — package table (with npm badges) + the "how they fit together" diagram + a data-family paragraph
• docs/packages/index.md — family table + diagram + a new "two engine families" section
• docs/guide/index.md — package table + diagram
• docs/.vitepress/config.ts — sidebar: AI family renamed, new data family group
• Architecture.md — "graduation candidates" -> "graduated (Phase 0, pending [orm #1] Decision: brand-consolidation with the Vike team (gate for #64) #66)", with the Rudder-adapter decision and the schema-graduates-with-orm finding recorded
• new docs/packages/orm.md + docs/packages/schema.md

schema is documented as preview / experimental (its API is still a spike and the compilers emit representative output). vitepress docs:build passes — links and the #adapters anchor resolve.

⚠️ HOLD MERGE

The docs site auto-deploys on merge to main, so this must not land until both are true:

1. [orm #1] Decision: brand-consolidation with the Vike team (gate for #64) #66 resolved — the Vike team confirms the @gemstack naming (vs keeping @universal-orm parallel). The names in these docs are provisional until then.
2. Packages published ([orm #2] Publish @universal-orm/core + universal-schema (core, together) #67/[orm #3] Publish @universal-orm/memory + @universal-orm/drizzle (adapters) #68) — they are private/unpublished today, so the npm version badges and npm install @gemstack/... lines would 404 if this went live now.

Merging early would advertise unpublished packages under a name not yet agreed. Ready to flip the moment both clear.

[suleimansh]

Closing per #66 (closed): the data layer stays @universal-orm and will NOT be presented as GemStack packages, so this docs PR is moot rather than something to rework. The engine packages themselves are being removed from this repo (see the removal PR) since vike-data / @universal-orm is the single source of truth.