chore: reorganize site pages and retire bulky generated artifacts

chore: reorganize site pages and retire bulky generated artifacts

The 3D text demo graduates from the Miscellaneous collection to its
own category directory (3D GFX/3D text/) with a dedicated page and a
root-page showcase section; its old collection-page section is removed
outright (no stub - the link checker proves nothing references the old
anchor). Every category page's "Back to BASIC applications collection"
link now carries the anchor of the root-page showcase section that
links down to it. AGENTS.org records both conventions.

3D Synthezier now versions its generated cities directly: city1.obj,
city2.obj and result.mtl are the published artifacts linked from the
doc page, replacing 25 MB of Blender conversions and the bin/backup
parser/output snapshots, all deleted along with the DOS batch
wrappers. The embedded street.obj example was regenerated with the
corrected face winding, and AGENTS.org notes that diagrams and
examples must be re-synced from real parser output after renames or
emission changes.

Universe explorer.bas received a second readability pass: systematic
descriptive names throughout (timerinit->timerInit, mkworld->
buildWorld, getCloudXYZ->getClusterPosition, disp->drawUniverse and
so on), behavior unchanged.

The Swapping 3D engine's letter font now has documented provenance:
objects/font/README.txt identifies the LTR vector glyphs byte-for-byte
as outlines of the ATI mach32/mach64 VGA BIOS 8x8 font traced by
mk3dfont.bas - not the IBM/SeaBIOS CP437 font used by crtbasic - and
putChar points at the note. The engine's runtime WORLD directory is
kept via .gitkeep with its contents ignored.

Tools/Update web site delegates org-to-HTML export to the shared
incremental exporter in svjatoslav_commons, re-exporting only changed
pages; the rsync upload now includes .obj/.mtl files and the export
state file is gitignored.