sky wheel: element contributor display; sign + house tooltips — TDD

sky_save now re-fetches from PySwiss server-side on save so stored
chart_data always carries enriched element format (contributors/stellia/
parades). New sky/data endpoint serves fresh PySwiss data to the My Sky
applet on load, replacing the stale inline json_script approach.

natus-wheel.js: sign ring slices (data-sign-name) and house ring slices
(data-house) now have click handlers with _activateSign/_activateHouse;
em-dash fallback added for classic elements with empty contributor lists.
Action URLs sky/preview, sky/save, sky/data lose trailing slashes.

Jasmine: T12 sign tooltip, T13 house tooltip, T14 enriched element
contributor display (symbols, Stellium/Parade formations, em-dash fallback).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/functional_tests/test_applet_my_sky.py

@@ -246,13 +246,13 @@ class MySkyAppletFormTest(FunctionalTest):
             const FIXTURE = """ + _json.dumps(_CHART_FIXTURE) + """;
             window._origFetch = window.fetch;
             window.fetch = function(url, opts) {
-                if (url.includes('/sky/preview/')) {
+                if (url.includes('/sky/preview')) {
                     return Promise.resolve({
                         ok: true,
                         json: () => Promise.resolve(FIXTURE),
                     });
                 }
-                if (url.includes('/sky/save/')) {
+                if (url.includes('/sky/save')) {
                     return Promise.resolve({
                         ok: true,
                         json: () => Promise.resolve({saved: true}),