fix(folders): root shows whole library + sidecar counts recurse

Two paired fixes for the folder tree on the timeline:

* +page.svelte: drop the `Path === ''` post-filter for the root entry.
  PhotoPrism's indexer always nests photos under YYYY/MM, so "photos
  whose Path is empty" is always the empty set in practice — the root
  entry looked broken instead of "whole library". Treat `/` as the
  unscoped view and rely on subfolder selections (now wildcarded via
  filters.svelte.ts) for narrowing.

* sidecar/handlers_folders.go: the per-folder count fan-out used
  `q=path:<x>`, the same exact-match operator that just got fixed in
  the web filter. Result: every year-level folder reported count=0
  in the sidebar. Switch to `q=path:"<x>*"` so the count reflects
  the whole subtree (dedupe by UID still in place).

sidecar/handlers_folders.go

@@ -231,12 +231,20 @@ func handleFolderCounts(pp *ppClient) gin.HandlerFunc {
 			go func() {
 				defer wg.Done()
 				defer func() { <-sem }()
-				// `path:` is non-recursive in PhotoPrism's q-DSL: matches
-				// direct children only. `merged=false` returns one row per
-				// File on disk, so HEIC + companion JPG count twice unless
-				// we dedupe by UID — which is what the old client-side
-				// code did, and what we keep doing here.
-				q := url.QueryEscape("path:" + path)
+				// `path:<x>` is an exact match in PhotoPrism's q-DSL —
+				// it matches only photos whose `photo_path` field equals
+				// <x>, not descendants. The indexer always nests photos
+				// under YYYY/MM, so an internal tree node like `2024` has
+				// zero direct children and reports a count of 0 unless we
+				// recurse. `path:<x>*` is the documented wildcard form and
+				// matches both `<x>` itself (no harm if empty) and every
+				// `<x>/...` descendant.
+				//
+				// `merged=false` still returns one row per File on disk,
+				// so HEIC + companion JPG count twice unless we dedupe by
+				// UID — which is what the old client-side code did, and
+				// what we keep doing here.
+				q := url.QueryEscape(`path:"` + path + `*"`)
 				resp, err := pp.call(c.Request.Context(), http.MethodGet,
 					"/api/v1/photos?count=1000&offset=0&merged=false&q="+q, token, nil)
 				if err != nil || !resp.OK {