Put the developer docs under docs/dev and index the folder for users first

docs/ had 26 developer documents flat beside the manual, and the two
audiences are very differently sized: most readers want the manual and
the gesture reference, a few want the register, the designs and the
measurements. The manual and gestures.md stay at the top; everything for
someone changing the code moves to docs/dev/, and the two documents that
name their own successors — the v0.1 milestone and the UI-refinement plan
— go to docs/dev/archive/ rather than being deleted, since both are still
cited. docs/README.md is the index, users first.

Every reference follows: code comments, Cargo manifests, the workflows,
the pre-commit hook, the bench and traceability tools (which locate the
repo root by docs/dev/requirements.md now), packaging, the Docker READMEs,
CLAUDE.md, CONTRIBUTING.md and the README. The matrix links one level
deeper and is regenerated. Links out of the moved documents into the tree
gain a level; a link checker over every Markdown file finds none broken.

models/LICENCE.md

@@ -39,11 +39,11 @@ bite the moment any hosted or server-side rendering appeared, and that is the
 thing to remember rather than rediscover.
 
 This was decided deliberately (D14), not arrived at by accident, and
-`docs/segmentation.md` §7 records the reasoning.
+`docs/dev/segmentation.md` §7 records the reasoning.
 
 ## Class vocabulary — a caveat worth reading
 
-`docs/segmentation.md` §4 specified YOLO **pretrained on ADE20K**, whose 150
+`docs/dev/segmentation.md` §4 specified YOLO **pretrained on ADE20K**, whose 150
 classes include the *stuff* categories that matter most in photography — sky,
 vegetation, water, wall, mountain.
 
@@ -108,7 +108,7 @@ the dataset licence restricts models trained on it by name.
 
 The bare 512 generator at a fixed `1×4×512×512`, six operator types; the
 tiling, the context and the blend are Rust (`dr_pano::fill`). Since
-2026-09-20 the shipped file is the fine-tune (`docs/panorama.md` §14),
+2026-09-20 the shipped file is the fine-tune (`docs/dev/panorama.md` §14),
 exported by `python -m infill.export` in `darkroom-infill`;
 `tools/export-migan.sh` still produces the stock generator from the upstream
 checkpoint, which the fine-tune starts from. The fine-tuned weights are a