gateway: nginx-hosts the full Swagger UI dist, core drops the fallback

Extends the theme-only alias into the full shape mara asked for on the
PR thread:

1. nix/packages/swagger-ui-dist.nix — plain vendored Swagger UI 5.17.14
   dist, sourced directly from the swagger-ui-dist npm package (same
   release the Rust utoipa-swagger-ui-vendored crate ships, verified
   via matching gitHead commit) rather than through Cargo.lock/cargo.
2. nix/packages/swagger-ui-theme.nix — overlays our 3 override files
   (index.html, hyperhive-theme.css, and now swagger-initializer.js)
   onto (1).
3. vhosts.nix's swaggerUiLocations now prefix-matches the whole
   /api/docs/ tree (not just 2 exact-match files) straight from (2),
   plus a `= /api/docs` redirect shim since hive-c0re's own redirect
   is going away too. /api/openapi.json (outside this prefix) keeps
   proxying to c0re unchanged — that's the one thing that stays
   dynamic.

New file swagger-initializer.js needed hand-verification: the plain
vendored copy hardcodes the swagger.io petstore demo URL.
utoipa-swagger-ui normally rewrites it per-request from a {{config}}
placeholder its own build.rs injects — since hive-c0re won't be
serving this file at all once its SwaggerUi mount is removed, that
rewrite has to be baked in statically here instead. Derived by
actually running build.rs's own two transforms (strip the default
layout: line, splice the Config JSON in place of the url/deepLinking
block) against the real vendored file, not typed from scratch —
verified byte-for-byte against what format_config() would produce for
hive-c0re's actual single-URL config, and checked with node --check.

Coordinated with damocles: he's taking the corresponding hive-c0re
side (drop the utoipa-swagger-ui dependency + SwaggerUi::new(...)
mount, keep only the plain /api/openapi.json route) once this lands.

Verified: nix fmt clean; nix build .#swagger-ui-theme succeeds, output
byte-matches the checked-in override files and node --check passes on
swagger-initializer.js; a full nixosSystem eval of nixosModules.default
resolves both new locations (/api/docs/ aliased to the right store
path, = /api/docs redirecting) with auth threaded through.

nix/host-modules/hive-c0re/options.nix

@@ -69,13 +69,13 @@
       type = lib.types.package;
       defaultText = lib.literalExpression "hyperhive.packages.\${system}.swagger-ui-theme";
       description = ''
-        Swagger UI re-theme static override files (see
-        `nix/packages/swagger-ui-theme.nix`; output has `index.html` +
-        `hyperhive-theme.css`). The hive-gateway module `alias`es these
-        two files straight from the store over `/api/docs/`, so a theme
-        tweak is a gateway config change — hive-c0re's own vendored
-        Swagger UI build is untouched. Override to ship a custom theme
-        (or the vendored default) without a hive-c0re rebuild.
+        Full Swagger UI static dist, hyperhive-themed (see
+        `nix/packages/swagger-ui-theme.nix`, built on
+        `nix/packages/swagger-ui-dist.nix`). hive-gateway serves this
+        whole tree directly at `/api/docs/` — hive-c0re hosts none of
+        it, only the dynamic `/api/openapi.json` route. Override to
+        ship a custom theme (or the plain vendored dist) without a
+        hive-c0re rebuild.
       '';
     };
     hyperhiveFlake = lib.mkOption {