fix(search): include Library source filter in shareable URL

The new library_source provenance filter wasn't serialised into the Share-view URL, so a
copied link lost the 'search results only' (or 'include search') selection. Add it as the
'source' param (emitted only in 'all' scope, omitted for the default 'organic').

frontend/src/lib/urlState.ts

@@ -9,6 +9,7 @@ const KEYS = [
   "show",
   "sort",
   "scope",
+  "source",
   "normal",
   "shorts",
   "live",
@@ -28,6 +29,9 @@ export function filtersToParams(f: FeedFilters): URLSearchParams {
   if (f.show && f.show !== "unwatched") p.set("show", f.show);
   if (f.sort && f.sort !== "newest") p.set("sort", f.sort);
   if (f.scope === "all") p.set("scope", "all");
+  // Library provenance filter (only meaningful in "all" scope); "organic" is the default.
+  if (f.scope === "all" && f.librarySource && f.librarySource !== "organic")
+    p.set("source", f.librarySource);
   if (!f.includeNormal) p.set("normal", "0");
   if (f.includeShorts) p.set("shorts", "1");
   if (f.includeLive) p.set("live", "1");
@@ -55,6 +59,10 @@ export function paramsToFilters(params: URLSearchParams, base: FeedFilters): Fee
   if (params.has("show")) f.show = params.get("show") || "unwatched";
   if (params.has("sort")) f.sort = params.get("sort") || "newest";
   if (params.has("scope")) f.scope = params.get("scope") === "all" ? "all" : "my";
+  if (params.has("source")) {
+    const s = params.get("source");
+    f.librarySource = s === "all" || s === "search" ? s : "organic";
+  }
   if (params.has("normal")) f.includeNormal = params.get("normal") !== "0";
   if (params.has("shorts")) f.includeShorts = params.get("shorts") === "1";
   if (params.has("live")) f.includeLive = params.get("live") === "1";