feat(m4): fixed tape line for length calibration (#99)

The photo pans, zooms, and tilts under a line that stays in the middle
of the frame. Scale is the source-pixel distance between the ticks
divided by the declared length, not the mask span.

frontend/package-lock.json

@@ -8,7 +8,6 @@
       "name": "slabuploader-frontend",
       "version": "0.1.0",
       "dependencies": {
-        "@neodrag/svelte": "2.3.3",
         "idb-keyval": "^6.3.0",
         "svelte": "^4.2.20"
       },
@@ -496,15 +495,6 @@
         "node": "^22.20 || ^24.12 || >=25"
       }
     },
-    "node_modules/@neodrag/svelte": {
-      "version": "2.3.3",
-      "resolved": "https://registry.npmjs.org/@neodrag/svelte/-/svelte-2.3.3.tgz",
-      "integrity": "sha512-avXzhrilsBsnMFljhVAQ7h+6hbSIrvRCJ61GCiGbGISkC1QOhjDCNvPZo2+7KVwiYrnUBx4NRH0kTIqrcxv9Lg==",
-      "license": "MIT",
-      "peerDependencies": {
-        "svelte": "^3.0.0 || ^4.0.0 || ^5.0.0"
-      }
-    },
     "node_modules/@playwright/test": {
       "version": "1.63.0",
       "resolved": "https://registry.npmjs.org/@playwright/test/-/test-1.63.0.tgz",