feat(dictionary): add Hachidori backend support

- Add backend selection, setup gating, Anki integration, and external host support
- Add launcher flags, documentation, packaging, and focused tests
- Open on-demand overlay modals on the first attempt

vendor/hachidori/third_party/hoshidicts/Package.swift

@@ -0,0 +1,58 @@
+// swift-tools-version: 6.2
+import PackageDescription
+
+let package = Package(
+    name: "hoshidicts",
+    platforms: [.iOS(.v18), .macOS(.v15)],
+    products: [
+        .library(name: "CHoshiDicts", targets: ["CHoshiDicts"]),
+        .executable(name: "hoshidicts", targets: ["hoshidicts"]),
+    ],
+    dependencies: [
+        .package(url: "https://github.com/facebook/zstd.git", from: "1.5.7"),
+    ],
+    targets: [
+        .target(
+            name: "CHoshiDicts",
+            dependencies: [
+                .product(name: "libzstd", package: "zstd"),
+            ],
+            path: ".",
+            sources: [
+                "src",
+                "external/libdeflate/lib",
+                "external/utf8proc/utf8proc.c",
+                "external/lzokay/lzokay.cpp",
+                "external/gumbo-parser/src",
+            ],
+            publicHeadersPath: "include",
+            cxxSettings: [
+                .headerSearchPath("include"),
+                .headerSearchPath("external/libdeflate"),
+                .headerSearchPath("external/libdeflate/lib"),
+                .headerSearchPath("external/utfcpp/source"),
+                .headerSearchPath("external/glaze/include"),
+                .headerSearchPath("external/xxHash"),
+                .headerSearchPath("external/unordered_dense/include"),
+                .headerSearchPath("external/utf8proc"),
+                .headerSearchPath("external/lzokay"),
+                .headerSearchPath("external/gumbo-parser/src"),
+                .unsafeFlags(["-Wno-missing-braces"]),
+            ],
+            swiftSettings: [
+                .interoperabilityMode(.Cxx)
+            ]
+        ),
+        .executableTarget(
+            name: "hoshidicts",
+            dependencies: ["CHoshiDicts"],
+            path: ".",
+            sources: ["cli/main.cpp"],
+            cxxSettings: [
+                .headerSearchPath("include"),
+                .headerSearchPath("external/utfcpp/source"),
+            ]
+        ),
+    ],
+    cxxLanguageStandard: .cxx2b
+)