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>

tsconfig.json

@@ -1,4 +1,11 @@
 {
   "files": [],
-  "references": [{ "path": "packages/core" }]
+  "references": [
+    {
+      "path": "packages/core"
+    },
+    {
+      "path": "packages/fls"
+    }
+  ]
 }