feat(ui): refine history graph visuals and layout

Refines history panel visuals and layout, including min width handling.
Removes the old branch visibility select in favor of a dialog button.
It also adds a graph connector to show primary branches.
Adds branch chips, icons, and hover effects to commits for clarity.

- History panel visuals and min width updated to improve layout.
- Removed branch visibility select; added dialog to customize branches.
- Branch chips and graph connectors enhanced with icons and hover effects.

src/lib/components/HistoryPanel.svelte

@@ -47,6 +47,7 @@
     "#ff7c9f", "#48c7d8", "#c5cf54", "#e18c55",
   ];
   const GRAPH_LANE = 18;
+  const GRAPH_REF_ARM = 16;
   const GRAPH_VISIBILITY_STORAGE_PREFIX = "gitlite.graphVisibility.v1:";
   const commitDateFormatter = new Intl.DateTimeFormat(undefined, {
     dateStyle: "medium",
@@ -411,12 +412,6 @@
     branchVisibilityMode = "focus";
   }
 
-  function changeBranchVisibilityMode(event: Event) {
-    const value = (event.currentTarget as HTMLSelectElement).value as BranchVisibilityMode;
-    branchVisibilityMode = value;
-    if (value === "custom") openBranchDialog();
-  }
-
   function openBranchDialog() {
     branchDialogOpen = true;
   }
@@ -760,21 +755,6 @@
     </div>
     {#if graphBranchNames.length > 0}
       <div class="section-head-actions">
-        <label class="graph-visibility-select" title="Choose which branches are shown in the graph">
-          <GitBranch size={13} aria-hidden="true" />
-          <span class="graph-visibility-label">Branches</span>
-          <select
-            aria-label="Branch visibility mode"
-            value={branchVisibilityMode}
-            onchange={changeBranchVisibilityMode}
-          >
-            <option value="focus">Focus</option>
-            <option value="local">Local</option>
-            <option value="all">All</option>
-            <option value="custom">Custom…</option>
-          </select>
-          <ChevronDown size={12} aria-hidden="true" />
-        </label>
         <button
           class="graph-branch-dialog-button"
           type="button"
@@ -782,6 +762,8 @@
           title="Customize visible branches"
           aria-label={`${visibleBranchCount} of ${graphBranchNames.length} branches visible. Customize branches.`}
         >
+          <GitBranch size={13} aria-hidden="true" />
+          Branches
           <span>{visibleBranchCount}/{graphBranchNames.length}</span>
         </button>
       </div>
@@ -837,6 +819,15 @@
                     vector-effect="non-scaling-stroke"
                   />
                 {/each}
+                {#if refSummary.primaryBranch}
+                  <path
+                    class="graph-ref-connector"
+                    d={`M ${graphColX(row.dotCol)} 50 L ${graphWidth - GRAPH_REF_ARM * 2} 50`}
+                    stroke={row.dotColor}
+                    stroke-width="1.5"
+                    vector-effect="non-scaling-stroke"
+                  />
+                {/if}
               </svg>
               <span
                 class="graph-dot"
@@ -851,9 +842,13 @@
             {/if}
           </div>
 
-          <div class="commit-body">
+          <div
+            class="commit-body"
+            class:has-branch-ref={Boolean(refSummary.primaryBranch)}
+            style={`--ref-lane-color:${row?.dotColor ?? GRAPH_COLORS[0]}`}
+          >
             {#if refSummary.primaryBranch || refSummary.primaryTag || refSummary.overflowCount > 0}
-              <div class="commit-ref-area" style={`--ref-lane-color:${row?.dotColor ?? GRAPH_COLORS[0]}`}>
+              <div class="commit-ref-area">
                 <div class="commit-ref-strip" aria-label="Commit references">
                   {#if refSummary.primaryBranch}
                     <span
@@ -862,7 +857,7 @@
                       class:remote={refSummary.primaryBranch.kind === "remote"}
                       title={branchDecorationTitle(refSummary.primaryBranch)}
                     >
-                      <i aria-hidden="true"></i>
+                      <GitBranch class="compact-ref-branch-icon" size={10} aria-hidden="true" />
                       <span>{refSummary.primaryBranch.label}</span>
                       {#if branchStatusLabel(refSummary.primaryBranch)}
                         <small class:up-to-date={Boolean(refSummary.primaryBranch.trackedRemote)}>