feat(fls): ZIP layer of the .fls codec

Reader and writer ported from filius-ipad with the same path policy,
limits and error codes; DEFLATE via fflate, cut at the declared size
like Apple Compression. 54 tests: the Swift archive rejection tests,
DEFLATE edge cases, and all 23 corpus files cross-checked against
fflate.unzipSync and round-tripped.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package-lock.json

@@ -471,6 +471,10 @@
       "resolved": "packages/core",
       "link": true
     },
+    "node_modules/@mdg-filius/fls": {
+      "resolved": "packages/fls",
+      "link": true
+    },
     "node_modules/@napi-rs/lzma-linux-x64-gnu": {
       "version": "1.5.1",
       "resolved": "https://registry.npmjs.org/@napi-rs/lzma-linux-x64-gnu/-/lzma-linux-x64-gnu-1.5.1.tgz",
@@ -1150,6 +1154,12 @@
         }
       }
     },
+    "node_modules/fflate": {
+      "version": "0.8.3",
+      "resolved": "https://registry.npmjs.org/fflate/-/fflate-0.8.3.tgz",
+      "integrity": "sha512-tbZNuJrLwGUp3zshBtdy4W+ORxZuIh8a5ilyIEQDC5rY1f3U20JMry0Ll3WBzU58EZKsEuJFXhb5gwv8CsPvgA==",
+      "license": "MIT"
+    },
     "node_modules/fsevents": {
       "version": "2.3.3",
       "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.3.3.tgz",
@@ -1645,6 +1655,14 @@
       "name": "@mdg-filius/core",
       "version": "0.0.0",
       "license": "GPL-3.0-only"
+    },
+    "packages/fls": {
+      "name": "@mdg-filius/fls",
+      "version": "0.0.0",
+      "license": "GPL-3.0-only",
+      "dependencies": {
+        "fflate": "^0.8.2"
+      }
     }
   }
 }