Port steps 0-1: scaffold, the oracle, and the pure bottom

Scaffolds frontend/ (shadow-cljs, reagent 1.2.0, re-frame 1.4.3) and ports
everything below the data model, with the JS kept as a numeric oracle.

  domain/landmarks  index tables, verbatim
  domain/ring       subsample, offset, simplicity
  domain/geom       similarity fit, procrustes, moving average
  domain/raster     indexed scanline fill, stencil, disc, rect
  domain/palette    the ramp, and the no-sampled-RGB rule

58 tests, 166 assertions. Parity with js/ on the identical 72-frame synthetic
track: fit-similarity, procrustes-mean, fit-residual, moving-average,
smooth-transforms, offset-ring and subsample-slots to 1e-9; the raster
pixel-for-pixel over the whole buffer.

Three deviations from the JS, each for a reason:

- synth.cljs jitters from a SEEDED generator, not Math.random. Parity is only
  checkable if both sides can be handed the same track, and a failing assertion
  has to be reproducible. `:rand-fn` takes the generator over, so oracle.mjs
  stubs js/Math.random and js/ itself stays untouched.

- raster/->rgba replaces toImageData. ImageData is a DOM type and domain/ may
  not touch the DOM; returning plain bytes also lets the
  no-intermediate-colours assertion run in node. ui/canvas wraps it later.

- offset-ring lives in domain/ring, not domain/geom, per architecture.md: it is
  an operation on an ordered traversal, not on a transform.

Step 1's "done" also names the swapped-iris vote, but pairIrises is in
pipeline.js and belongs to step 7. The precondition is asserted instead --
`:swap-iris` really does move both blocks -- so the vote will have a track that
disagrees with it when it arrives.

One finding, recorded in full in the test that measures it: smooth-transforms
buys nothing on the synthetic track. Against jitter-free ground truth, radius 1
helps by 17% on one noise realisation and hurts by 0.5% on another, so its
benefit is within noise; from radius 2 up the cost is unambiguous, and by radius
5 the filter is below the true motion's own high-frequency energy, i.e.
smoothing away performance. The test pins the shape of the knob rather than a
preferred value. This may say more about the synth's jitter being unrealistically
small (+/-0.001 normalised) than about the knob; step 6 settles it on real
footage.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/shadow-cljs.edn

@@ -0,0 +1,41 @@
+;; Two builds and no more:
+;;
+;;   app   the tool. Output goes straight into the Django staticfiles tree, so
+;;         `python manage.py runserver` and `shadow-cljs watch app` are the whole
+;;         dev loop with nothing copying files between them.
+;;   test  :node-test, because everything below `ui/` and `fx/` is pure and has
+;;         no business needing a browser to be asserted about. The canvas-facing
+;;         parts get asserted through domain/raster's byte buffer instead, which
+;;         is what the JS selftest already did.
+{:source-paths ["src" "test"]
+
+ :dependencies [[reagent "1.2.0"]
+                [re-frame "1.4.3"]]
+
+ ;; Dev server for the CLJS half, on a different port from serve.py (8777) so the
+ ;; old tool and the port can run side by side — which is the whole point of
+ ;; keeping js/ around as the numeric oracle.
+ ;;
+ ;; Two roots: `public` holds the host page, `..` is the repo root so the bundle
+ ;; at /static/arthur/js/ resolves, and so manifest.json, audio.wav and frames/
+ ;; are reachable when step 6 needs real footage.
+ ;;
+ ;; THE ORDER IS LOAD-BEARING. The repo root has an index.html too — the old
+ ;; tool's — so with `..` first, /index.html would quietly serve the prototype
+ ;; instead of the port. That would look like the CLJS build having regressed to
+ ;; a suspiciously complete tool rather than like a misconfigured server.
+ ;;
+ ;; Open /index.html, not /. This shadow-cljs does no directory-index resolution,
+ ;; so bare / is a 404 whatever the roots are. Django serves the page from step 9
+ ;; and this whole key goes away.
+ :dev-http {8778 ["public" ".."]}
+
+ :builds
+ {:app  {:target     :browser
+         :output-dir "../static/arthur/js"
+         :asset-path "/static/arthur/js"
+         :modules    {:main {:init-fn arthur.core/init}}}
+
+  :test {:target    :node-test
+         :output-to "out/node-tests.js"
+         :ns-regexp "-test$"}}}