fix(filters): browse with no rules works, popup under the input, no sticky headers (user report)

- Blank typed queries rode the STATIC autocomplete path for the classic
  six fields, where a single space similarity-matches into nothing —
  clicking an empty value box with no other filters said 'No matching
  values' in a library full of values. Blank = browse now always rides
  the composed engine (which trims and answers the top values); static
  keeps its pinned contract for real typed queries. Regression-pinned:
  browse with no rules lists the field's values.
- The value popup now drops BELOW the input (top: 100%), not over it.
- Field-menu group headers lost position:sticky — the search box alone
  stays pinned.

internal/handlers/media.go

@@ -2648,9 +2648,14 @@ func (mh *MediaHandler) handleFieldValuesSearch(c *echo.Context, userID pgtype.U
 		tree = t
 	}
 
-	// Static path: the classic six with no rule tree (unchanged
-	// contract — the tag-dropdown island and deep links still ride it).
-	staticSix := tree == nil
+	// Static path: the classic six with a REAL typed query and no rule
+	// tree (unchanged contract — the tag-dropdown island and deep links
+	// still ride it). A BLANK typed query is BROWSE (the builder's
+	// click-the-box top-values list): the static queries would
+	// similarity-match a single space into nothing, so browse rides the
+	// composed engine, which trims the query and answers the top values
+	// under the rules.
+	staticSix := tree == nil && strings.TrimSpace(searchQuery) != ""
 	if staticSix {
 		switch fieldType {
 		case "author", "genre", "tags", "narrator", "series", "language":