fix: floating mini-chat overlay style + weather precip fallback

- KnowledgeView mini-chat: replace harsh border-top with upward box-shadow
  and rounded top corners (16px); remove padding-bottom from content area
  so widget truly overlays cards without pushing layout; add collapse
  toggle (chevron) that hides messages without closing the conversation
- WeatherCard: show precip_mm as fallback when precipitation_probability_max
  is null but actual rainfall is expected (Open-Meteo omits probability for
  some forecast days even when rain is shown)
- Pass precip_mm through weather service → frontend type definitions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/BriefingView.vue

@@ -36,7 +36,7 @@ interface WeatherData {
   yesterday_high: number | null
   yesterday_low: number | null
   wind_unit?: string
-  forecast: { day: string; condition: string; high: number; low: number; precip_probability: number | null; windspeed_max: number }[]
+  forecast: { day: string; condition: string; high: number; low: number; precip_probability: number | null; precip_mm: number | null; windspeed_max: number }[]
 }
 
 const chatStore = useChatStore()

frontend/src/views/KnowledgeView.vue

@@ -136,6 +136,7 @@ function toggleGraph() {
 
 const chatInput = ref("");
 const chatOpen = ref(false);
+const chatCollapsed = ref(false);
 const chatConvId = ref<number | null>(null);
 const chatSending = ref(false);
 const chatMessages = computed(() => {
@@ -437,8 +438,8 @@ onUnmounted(() => {
 
     <!-- Floating mini-chat -->
     <div class="minichat" :class="{ 'minichat--open': chatOpen }">
-      <!-- Message history (shown when chatOpen) -->
-      <div v-if="chatOpen" class="minichat-messages" ref="chatScrollEl">
+      <!-- Message history (shown when chatOpen and not collapsed) -->
+      <div v-if="chatOpen && !chatCollapsed" class="minichat-messages" ref="chatScrollEl">
         <template v-if="chatMessages.length === 0 && !chatStore.streaming">
           <div class="minichat-welcome">Ask me anything about your notes, tasks, or ideas.</div>
         </template>
@@ -495,6 +496,17 @@ onUnmounted(() => {
             title="Send"
           >&uarr;</button>
         </div>
+        <button
+          v-if="chatOpen"
+          class="btn-close-chat"
+          @click="chatCollapsed = !chatCollapsed"
+          :title="chatCollapsed ? 'Expand chat' : 'Collapse chat'"
+        >
+          <svg width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5">
+            <polyline v-if="chatCollapsed" points="18 15 12 9 6 15"/>
+            <polyline v-else points="6 9 12 15 18 9"/>
+          </svg>
+        </button>
         <button
           v-if="chatOpen"
           class="btn-close-chat"
@@ -633,7 +645,6 @@ onUnmounted(() => {
   flex-direction: column;
   overflow: hidden;
   min-width: 0;
-  padding-bottom: 64px; /* space for minichat input */
 }
 
 /* ── Toolbar ─────────────────────────────────────────────── */
@@ -904,9 +915,10 @@ onUnmounted(() => {
   z-index: 20;
   display: flex;
   flex-direction: column;
-  border-top: 1px solid var(--color-border, rgba(255,255,255,0.06));
   background: var(--color-bg-secondary);
-  transition: all 0.2s;
+  border-radius: 16px 16px 0 0;
+  box-shadow: 0 -8px 32px rgba(0,0,0,0.35), 0 -1px 0 rgba(255,255,255,0.05);
+  transition: box-shadow 0.2s;
 }
 .knowledge-root.graph-open .minichat {
   right: 420px;
@@ -918,8 +930,9 @@ onUnmounted(() => {
   display: flex;
   flex-direction: column;
   gap: 8px;
-  background: var(--color-bg);
-  border-bottom: 1px solid var(--color-border, rgba(255,255,255,0.06));
+  background: transparent;
+  border-bottom: 1px solid rgba(255,255,255,0.05);
+  border-radius: 16px 16px 0 0;
 }
 .minichat-welcome {
   color: var(--color-muted);