docs(stammbaum): ADR-026 custom viewBox pan/zoom + glossary terms (#692)

Record the reversal of OQ-007 (build custom over the existing viewBox rather
than adopt the panzoom library) and add pan/zoom view-state + fit-to-screen
glossary entries.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/GLOSSARY.md

@@ -125,6 +125,10 @@ _Not to be confused with [parented](#parented-layout)_ — loose is the absence
 
 **canonical fixture** (Stammbaum) — `frontend/src/lib/person/genealogy/__fixtures__/stammbaum.json`, a pinned `/api/network` snapshot used by `buildLayout.test.ts` for structural-property assertions against real data. Captured locally via `frontend/scripts/capture-network-fixture.mjs` with explicit credentials and a localhost backend; never invoked from CI. Sanity-gated by `validateFixture.ts` (≥ 50 nodes / ≥ 5 generations / ≥ 1 SPOUSE_OF edge / ≥ 1 multi-spouse person).
 
+**pan/zoom view state** `[#692]` — the `{ x, y, z }` triple (`PanZoomState` in `frontend/src/lib/person/genealogy/panZoom.ts`) describing the Stammbaum canvas position: `x`/`y` are pan offsets applied to the SVG viewBox centre, `z` is the zoom factor (clamped 0.25–3.0). Mirrored into the shareable URL as `?cx&cy&z` and seeded server-side from those params. See [ADR-026](adr/026-stammbaum-custom-viewbox-pan-zoom.md).
+
+**fit-to-screen** `[user-facing, #692]` — the Stammbaum control (`⤢`) and initial state that frames the whole tree in the viewport. Because the base viewBox already encloses the layout at `z=1`, fit-to-screen is simply the default view `{x:0, y:0, z:1}`.
+
 ---
 
 ## Other Domain Terms