feat(git): commit graph in history view and cross-spawn everywhere

- render a VSCode-style commit graph in the source control history:
  lane-assignment algorithm, SVG strip with colored rails, merge and
  branch curves, commit dots, and branch/tag badges per commit
- /commits returns parents and ref decorations across all branches
  (--branches --remotes --tags --topo-order) using unit-separator
  fields so pipes in commit subjects can't break parsing
- collect stats via a single --shortstat pass instead of one
  `git show --stat` call per commit; raise the history limit to 50
- replace child_process spawn with cross-spawn in all runtimes,
  routes, and services: it resolves .cmd shims and PATHEXT on
  Windows (fixing taskmaster's npx invocations) and delegates to
  native spawn elsewhere, removing the per-file win32 ternaries
- unit tests for the log parser and lane assignment

src/components/git-panel/view/history/CommitGraphStrip.tsx

@@ -0,0 +1,95 @@
+import type { CommitGraphRow } from '../../utils/commitGraph';
+import { laneColor } from '../../utils/commitGraph';
+
+// Geometry: each lane is a fixed-width column; the commit dot sits at NODE_Y
+// inside a fixed-height top zone (matching the collapsed row header), and
+// plain rails continue below it so lines stretch through expanded content.
+const LANE_WIDTH = 12;
+const NODE_ZONE_HEIGHT = 56;
+const NODE_Y = 28;
+const NODE_RADIUS = 3.5;
+const STROKE_WIDTH = 2;
+
+const laneX = (lane: number) => lane * LANE_WIDTH + LANE_WIDTH / 2;
+
+type CommitGraphStripProps = {
+  row: CommitGraphRow;
+};
+
+export default function CommitGraphStrip({ row }: CommitGraphStripProps) {
+  const width = row.laneCount * LANE_WIDTH;
+  const nodeX = laneX(row.nodeLane);
+  const nodeColor = laneColor(row.nodeLane);
+
+  return (
+    <div aria-hidden className="relative shrink-0 self-stretch overflow-hidden" style={{ width }}>
+      <svg
+        className="absolute left-0 top-0"
+        width={width}
+        height={NODE_ZONE_HEIGHT}
+        fill="none"
+      >
+        {/* Lines passing straight through the row */}
+        {row.passThrough.map((lane) => (
+          <path
+            key={`pass-${lane}`}
+            d={`M ${laneX(lane)} 0 V ${NODE_ZONE_HEIGHT}`}
+            stroke={laneColor(lane)}
+            strokeWidth={STROKE_WIDTH}
+          />
+        ))}
+
+        {/* The node's own lane arriving from above / continuing below */}
+        {row.hasTopContinuation && (
+          <path d={`M ${nodeX} 0 V ${NODE_Y}`} stroke={nodeColor} strokeWidth={STROKE_WIDTH} />
+        )}
+        {row.hasParentContinuation && (
+          <path d={`M ${nodeX} ${NODE_Y} V ${NODE_ZONE_HEIGHT}`} stroke={nodeColor} strokeWidth={STROKE_WIDTH} />
+        )}
+
+        {/* Extra children merging into the node from the row above */}
+        {row.inbound.map((lane) => (
+          <path
+            key={`in-${lane}`}
+            d={`M ${laneX(lane)} 0 Q ${laneX(lane)} ${NODE_Y} ${nodeX} ${NODE_Y}`}
+            stroke={laneColor(lane)}
+            strokeWidth={STROKE_WIDTH}
+          />
+        ))}
+
+        {/* Extra parents branching out of the node toward the row below */}
+        {row.outbound.map((lane) => (
+          <path
+            key={`out-${lane}`}
+            d={`M ${nodeX} ${NODE_Y} Q ${laneX(lane)} ${NODE_Y} ${laneX(lane)} ${NODE_ZONE_HEIGHT}`}
+            stroke={laneColor(lane)}
+            strokeWidth={STROKE_WIDTH}
+          />
+        ))}
+
+        {/* Commit dot — slightly larger for merge/fork points */}
+        <circle
+          cx={nodeX}
+          cy={NODE_Y}
+          r={row.inbound.length > 0 || row.outbound.length > 0 ? NODE_RADIUS + 0.5 : NODE_RADIUS}
+          fill={nodeColor}
+        />
+      </svg>
+
+      {/* Rails continuing below the node zone (through expanded content) */}
+      {row.bottomLanes.map((lane) => (
+        <div
+          key={`rail-${lane}`}
+          className="absolute"
+          style={{
+            left: laneX(lane) - STROKE_WIDTH / 2,
+            top: NODE_ZONE_HEIGHT,
+            bottom: 0,
+            width: STROKE_WIDTH,
+            backgroundColor: laneColor(lane),
+          }}
+        />
+      ))}
+    </div>
+  );
+}