fix(macos): enable x86_64 cross-compilation

- Upgrade rust_cast 0.18.1 → 0.21 (switches from openssl to rustls,
  removing the openssl-sys dependency that blocked x86_64 cross-compile)
- Split mupdf sys-lib features to Linux-only (on macOS there are no GTK
  symbol conflicts, and system libs don't support x86_64 cross-compile
  from Apple Silicon)
- Update release-macos workflow to build both aarch64 and x86_64 DMGs
  using a matrix strategy

src-tauri/Cargo.lock

@@ -4417,9 +4417,9 @@ dependencies = [
 
 [[package]]
 name = "protobuf"
-version = "3.2.0"
+version = "3.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b55bad9126f378a853655831eb7363b7b01b81d19f8cb1218861086ca4a1a61e"
+checksum = "d65a1d4ddae7d8b5de68153b48f6aa3bba8cb002b243dbdbc55a5afbc98f99f4"
 dependencies = [
  "once_cell",
  "protobuf-support",
@@ -4428,9 +4428,9 @@ dependencies = [
 
 [[package]]
 name = "protobuf-codegen"
-version = "3.2.0"
+version = "3.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0dd418ac3c91caa4032d37cb80ff0d44e2ebe637b2fb243b6234bf89cdac4901"
+checksum = "5d3976825c0014bbd2f3b34f0001876604fe87e0c86cd8fa54251530f1544ace"
 dependencies = [
  "anyhow",
  "once_cell",
@@ -4443,12 +4443,12 @@ dependencies = [
 
 [[package]]
 name = "protobuf-parse"
-version = "3.2.0"
+version = "3.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9d39b14605eaa1f6a340aec7f320b34064feb26c93aec35d6a9a2272a8ddfa49"
+checksum = "b4aeaa1f2460f1d348eeaeed86aea999ce98c1bded6f089ff8514c9d9dbdc973"
 dependencies = [
  "anyhow",
- "indexmap 1.9.3",
+ "indexmap 2.13.0",
  "log",
  "protobuf",
  "protobuf-support",
@@ -4459,9 +4459,9 @@ dependencies = [
 
 [[package]]
 name = "protobuf-support"
-version = "3.2.0"
+version = "3.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a5d4d7b8601c814cfb36bcebb79f0e61e45e1e93640cf778837833bbed05c372"
+checksum = "3e36c2f31e0a47f9280fb347ef5e461ffcd2c52dd520d8e216b52f93b0b0d7d6"
 dependencies = [
  "thiserror 1.0.69",
 ]
@@ -5306,18 +5306,19 @@ dependencies = [
 
 [[package]]
 name = "rust_cast"
-version = "0.18.1"
+version = "0.21.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7c9b210a559ed66ebb5096ebb754ad14e197bf8954c029bae6bfc82f0f51e460"
+checksum = "235d09067a35143d271fdeaf28298b4f729b5da50abdbf3b9e6395262d8bc7a9"
 dependencies = [
  "byteorder",
  "log",
- "openssl",
  "protobuf",
  "protobuf-codegen",
+ "rustls",
+ "rustls-native-certs",
  "serde",
- "serde_derive",
  "serde_json",
+ "thiserror 2.0.18",
 ]
 
 [[package]]
@@ -5391,6 +5392,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "758025cb5fccfd3bc2fd74708fd4682be41d99e5dff73c377c0646c6012c73a4"
 dependencies = [
  "aws-lc-rs",
+ "log",
  "once_cell",
  "ring",
  "rustls-pki-types",
@@ -5399,6 +5401,18 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "rustls-native-certs"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "612460d5f7bea540c490b2b6395d8e34a953e52b491accd6c86c8164c5932a63"
+dependencies = [
+ "openssl-probe",
+ "rustls-pki-types",
+ "schannel",
+ "security-framework",
+]
+
 [[package]]
 name = "rustls-pki-types"
 version = "1.14.0"