Replace v1 with v2 codebase

Full rewrite: swap out the v1 framework (src/, controllers/, views/,
twig/, sass/, skeleton/) for the working v2 codebase from phpproject
(App/, novaconium/, public/).

App/sass/_colors.sass

@@ -0,0 +1,25 @@
+// This project's color palette — overrides
+// novaconium/sass/defaults/_colors.sass's framework defaults. Same
+// mechanism as App/pages/ overriding novaconium/pages/: same relative
+// filename, checked first on the Sass load path. Change any of these and
+// recompile (see /admin/docs/styling) to reskin the whole site from one
+// file. Delete this file entirely to fall back to the framework's
+// default palette instead.
+$bg: #14181c
+$surface: #1b2126
+$text-color: #e7ebee
+$muted-color: #98a3ac
+$border-color: #2a3238
+$accent: #2dd4bf
+$accent-hover: #5eead4
+
+// Light theme, used when a visitor toggles it (see the theme-toggle
+// button in novaconium/pages/_layout/nav.twig) — same seven names with a
+// -light suffix, same override mechanism.
+$bg-light: #ffffff
+$surface-light: #f1f4f6
+$text-color-light: #14181c
+$muted-color-light: #5b6570
+$border-color-light: #d8dee3
+$accent-light: #0f9488
+$accent-hover-light: #0c7a70