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).

templates/bookshelf.templ

@@ -183,9 +183,7 @@ templ BookShelf(
 										<div>
 											<template x-if="row.type === 'groupOpen'">
 												<div :class="row.depth > 0 ? 'fb-nested' : ''" class="flex items-center gap-1.5 flex-wrap py-1" :style="`margin-left:${row.depth * 14}px`">
-													<span class="text-[11px] font-semibold uppercase tracking-wide" style="color: var(--text-secondary)" x-text="'Match'"></span>
-													<button type="button" class="fb-mode-btn" :class="row.group.mode === 'all' ? 'fb-mode-active' : ''" @click="setGroupMode(row.path, 'all')" title="Every rule in this group must match">AND</button>
-													<button type="button" class="fb-mode-btn" :class="row.group.mode === 'any' ? 'fb-mode-active' : ''" @click="setGroupMode(row.path, 'any')" title="Any rule in this group can match">OR</button>
+													<span class="text-[11px] font-semibold uppercase tracking-wide" style="color: var(--text-secondary)" x-text="row.depth === 0 ? 'Match' : 'Group'"></span>
 													<span class="flex-1"></span>
 													<button type="button" class="fb-mini-btn" @click="addRule(row.path)">+ rule</button>
 													<button type="button" class="fb-mini-btn" @click="addGroup(row.path)">+ group</button>
@@ -194,7 +192,7 @@ templ BookShelf(
 											</template>
 											<template x-if="row.type === 'rule'">
 												<div :class="row.depth > 0 ? 'fb-nested' : ''" class="flex items-center gap-1.5 flex-wrap py-0.5" :style="`margin-left:${(row.depth + 1) * 14}px`">
-													<button type="button" class="fb-connective fb-connective-btn" x-show="!row.isFirst" x-text="row.connective" @click="toggleGroupMode(row.path.slice(0, -1))" title="Switch this group between AND / OR"></button>
+													<button type="button" class="fb-connective fb-connective-btn" :class="row.chipClickable ? '' : 'fb-chip-static'" x-show="!row.isFirst" x-text="row.chip" @click="if (row.chipClickable) toggleRuleConnective(row.path)" :title="row.chipClickable ? 'Switch this rule between AND / OR' : 'This rule joins with ' + row.chip"></button>
 													<!-- field picker: grouped menu -->
 													<div class="relative">
 														<button type="button" class="fb-picker" :class="{'fb-picker-active': row.rule.field !== ''}" @click="toggleMenu(row.key + ':field')" x-text="fieldLabelOf(row.rule.field)"></button>