fix: remove view max-width constraints; widen graph panel

- Drop max-width from .knowledge-root so the graph panel can use the full
  viewport width without hitting a cap
- Drop max-width from .chat-page (message bubbles are already self-constraining)
- Increase normal graph panel width 420px → 500px
- Increase expanded width to min(960px, 60vw) so it scales with the viewport
  and updates minichat right-offset to match

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

frontend/src/views/ChatView.vue

@@ -1034,9 +1034,6 @@ onUnmounted(() => {
   display: flex;
   height: 100%;
   overflow: hidden;
-  max-width: 1600px;
-  width: 100%;
-  margin: 0 auto;
 }
 
 .chat-sidebar {

frontend/src/views/KnowledgeView.vue

@@ -545,9 +545,6 @@ onUnmounted(() => {
   flex-direction: column;
   height: calc(100vh - var(--header-height, 56px));
   overflow: hidden;
-  max-width: 1600px;
-  width: 100%;
-  margin: 0 auto;
 }
 
 /* ── Today bar ───────────────────────────────────────────── */
@@ -890,7 +887,7 @@ onUnmounted(() => {
 
 /* ── Graph panel ─────────────────────────────────────────── */
 .graph-panel {
-  width: 420px;
+  width: 500px;
   flex-shrink: 0;
   border-left: 1px solid var(--color-border, rgba(255,255,255,0.06));
   display: flex;
@@ -899,7 +896,7 @@ onUnmounted(() => {
   transition: width 0.2s ease;
 }
 .graph-panel.expanded {
-  width: 700px;
+  width: min(960px, 60vw);
 }
 .graph-panel-header {
   display: flex;
@@ -947,11 +944,11 @@ onUnmounted(() => {
   transition: box-shadow 0.2s;
 }
 .knowledge-root.graph-open .minichat {
-  right: 420px;
+  right: 500px;
   transition: right 0.2s ease;
 }
 .knowledge-root.graph-open.graph-expanded .minichat {
-  right: 700px;
+  right: min(960px, 60vw);
 }
 .minichat-messages {
   max-height: 360px;