Replace hand-rolled spatial canvas drag with Konva

The custom pointer-capture + frozen-camera drag math was fragile and
felt worse than before. Konva handles the drag gesture itself; the
"me" node's screen position stays pinned to the stage center via
dragBoundFunc + a worldLayer offset that recenters on every dragmove,
so the world pans under the avatar instead of the avatar drifting off
center. Grid, peers, and the audible-range circle all live in the same
world-space layer so they pan together.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package-lock.json

@@ -16,6 +16,7 @@
         "@opentelemetry/sdk-logs": "^0.222.0",
         "@opentelemetry/sdk-node": "^0.222.0",
         "@opentelemetry/semantic-conventions": "^1.43.0",
+        "konva": "^10.6.0",
         "matrix-js-sdk": "^42.4.0",
         "ws": "^8.18.0"
       },
@@ -3940,6 +3941,38 @@
         "bignumber.js": "^9.0.0"
       }
     },
+    "node_modules/konva": {
+      "version": "10.6.0",
+      "resolved": "https://registry.npmjs.org/konva/-/konva-10.6.0.tgz",
+      "integrity": "sha512-6dyI91lZTx2mDu9DRo5zrT2Pg+Q3TFeyLfGQSAPJMhfvKjelbjPnTJimYQISam/EW+g0+pjLk/yztJKpSuxFPQ==",
+      "funding": [
+        {
+          "type": "patreon",
+          "url": "https://www.patreon.com/lavrton"
+        },
+        {
+          "type": "opencollective",
+          "url": "https://opencollective.com/konva"
+        },
+        {
+          "type": "github",
+          "url": "https://github.com/sponsors/lavrton"
+        }
+      ],
+      "license": "MIT",
+      "peerDependencies": {
+        "canvas": "^3.0.0",
+        "skia-canvas": "^3.0.0"
+      },
+      "peerDependenciesMeta": {
+        "canvas": {
+          "optional": true
+        },
+        "skia-canvas": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/lightningcss": {
       "version": "1.33.0",
       "resolved": "https://registry.npmjs.org/lightningcss/-/lightningcss-1.33.0.tgz",