docs: pin QGIS 4.2.3 and compute the projected origin with PROJ

QGIS stable is 4.2.3 on the current KDE runtime; the stale 3.28.9 lts install
stays flagged for removal. PROJ 9.9.0 from that flatpak turns the recorded
origin into E 376515.389 / N 3774224.083 (NAD83 UTM 11N), with six control
points whose projected spans reproduce the OSM footprint measurements. Engine
decision recorded: 5.8.4 is downloading, 5.2.0 stays only as a fallback.

ROADMAP.md

@@ -29,7 +29,7 @@ Status detail in [Docs/setup.md](Docs/setup.md); workstation audit in [Docs/envi
 - [x] Save a versioned OSM extract; document date, bounds, and source in `Geo/`.
 - [-] Acquire separately licensed elevation data if needed. Needed: measured relief is 3.94 m over the block (`Geo/verification/2026-11-06-elevation.md`). Source chosen: USGS 3DEP 1 m DEM, public domain, vertical datum NAVD88.
 - [ ] Download the 3DEP 1 m DEM for the demo bounds, reproject it to EPSG:26911 with the recorded origin and vertical datum, and record the source, clip bounds, and checksum in `Geo/`.
-- [-] In QGIS, set a suitable local projected CRS (e.g. EPSG:26911) and record a local origin. CRS and origin point are fixed in `Geo/manifests/local-origin.md`; the EPSG:26911 easting/northing still has to be computed with PROJ/QGIS, which also confirms the transformation.
+- [x] In QGIS, set a suitable local projected CRS (e.g. EPSG:26911) and record a local origin. EPSG:26911, origin and projected easting/northing are recorded in `Geo/manifests/local-origin.md` with PROJ 9.9.0 control points; QGIS 4.2.3 is installed for the DEM reprojection step.
 - [x] Verify the address, building footprints, and demo boundaries for 6840 Hollywood Blvd against source data.
 - [ ] Import OSM blockouts through Blosm; clean and detail them in Blender.
 - [ ] Preserve geographic coordinates in metadata; define explicit meter→centimeter conversion to local Unreal coordinates.