feat(web): templ partials replace the last UI twins (collections grid, conflicts list)

Both pages had a templ render (initial load) and a TypeScript twin
(innerHTML rebuild on refresh) of the same fragment. The twins are
deleted; the server-rendered markup is now the only markup.

- collections: the library switcher swaps in the new books-grid partial
  (GET /collections/:id/books-grid) instead of re-rendering cards from
  the /api/collections JSON. Book loading is extracted into
  Config.loadCollectionBooks, shared verbatim by the page and the
  partial (smart / dashboard-query / manual branches, family-lens
  scoping via resolveLibrary + UserVisibleLibraryIDs) so the two cannot
  drift.
- conflicts: resolve/dismiss refreshes swap the new list partial
  (GET /conflicts/list) with the stats bar as an out-of-band swap,
  instead of the TS twin — which rendered a degraded card (no
  checkboxes, no timestamps), pointed at a window.showResolveModal that
  does not exist, and updated stats via element ids the SSR never had.
- shims.d.ts: window.htmx typing (ajax/process) for TS callers.

Visibility note: the books-grid partial inherits its family-lens
scoping from the shared loader (identical to the detail page); a
dedicated hidden-library pin test for the partial route is still worth
adding in the next test pass.

web/src/shims.d.ts

@@ -1,2 +1,22 @@
 declare module "markdown-it-footnote";
 declare module "turndown-plugin-gfm";
+
+// htmx is loaded as a classic script on every page and used from TS for
+// partial swaps (rendering-ownership rule: templ renders, JS swaps).
+interface HtmxAjaxOptions {
+  target?: string;
+  swap?: string;
+  values?: Record<string, string>;
+  headers?: Record<string, string>;
+}
+
+interface Window {
+  htmx: {
+    ajax(
+      method: string,
+      url: string,
+      options?: HtmxAjaxOptions,
+    ): Promise<boolean>;
+    process(element: Element): void;
+  };
+}