feat(filters): per-row AND/OR (Excel-style chips) + browse-on-click value menus (user report)

- Per-rule connectives: the chip before each rule flips that rule
  between AND and OR — OR-joined neighbors merge into an invisible
  OR-block, AND pulls them back out. The tree stays the single source
  of truth (implicit blocks are a client marker the server ignores),
  so deep links, saved filters, and the composed engine are untouched.
  Group-mode pills are gone; explicit groups remain as pure structure
  (+ group). Compile limit, same as Excel: flat chips express
  AND-of-OR-groups; a top-level OR of AND-blocks still needs nesting.
- Browse-on-click: clicking an empty value box now fetches the field's
  top values UNDER the other rules (blank typed = browse, not a
  similarity filter) — 'assign an author, click Publisher, see their
  publishers' without typing. Server: the composed suggestion engine
  trims the typed query; client: the >=2-char guard no longer blocks
  the empty query, browse limit 15 vs 8 while typing.
- Tests: the browse case pinned (blank sentinel + rules → the field's
  values under those rules, zero-match values absent).

internal/services/filter_query.go

@@ -863,6 +863,10 @@ func (s *SearchService) ComposedFieldValues(ctx context.Context, p ComposedSugge
 	if p.Limit <= 0 {
 		p.Limit = 50
 	}
+	// A blank typed query means BROWSE (the user clicked the value box
+	// to see what exists under the other rules) — not a similarity
+	// filter for a single space.
+	p.Typed = strings.TrimSpace(p.Typed)
 
 	b := newFilterBuilder(p.UserID)
 	typedBind := b.bind(p.Typed)