feat(poc/bridge): add flutter_rust_bridge hello spike

Proof-of-concept proving the Flutter/Rust bridge exit criterion from
docs/architecture/proof-of-concept-plan.md §2:
  "Flutter can call Rust and receive event stream data."

The spike exposes one synchronous fallible command (greet) returning
a typed GreetResult / GreetError DTO, and one async event stream
(counter_stream) emitting typed CounterTick events. The Flutter app
demonstrates both flows on a Material 3 surface; the headless test
suite in test/poc_verification_test.dart exercises the same API
directly through dart:ffi.

Verified on 2026-05-13 (Linux desktop, Flutter 3.41.9 / Dart 3.11.5,
flutter_rust_bridge 2.12.0, Rust 1.95). All three tests pass:
  - greet() returns typed result for valid input
  - greet() surfaces typed error for empty input
  - counterStream() delivers the expected event sequence

Authority: PoC plan §2, DEC-014 (typed Flutter/Rust bridge),
SAD-068, SDD-079, SysDes-049.
Naming note: the PoC plan lists this as flutter-rust-bridge-hello,
but Dart pubspec.yaml package names require underscores; the
directory uses underscores accordingly.
Not product code; not promoted into chanora_bridge.

Layout note: includes the full Flutter platform scaffold (android,
ios, macos, windows, web, linux). Only the Linux desktop target has
been built and verified.

poc/flutter_rust_bridge_hello/windows/runner/Runner.rc

@@ -0,0 +1,121 @@
+// Microsoft Visual C++ generated resource script.
+//
+#pragma code_page(65001)
+#include "resource.h"
+
+#define APSTUDIO_READONLY_SYMBOLS
+/////////////////////////////////////////////////////////////////////////////
+//
+// Generated from the TEXTINCLUDE 2 resource.
+//
+#include "winres.h"
+
+/////////////////////////////////////////////////////////////////////////////
+#undef APSTUDIO_READONLY_SYMBOLS
+
+/////////////////////////////////////////////////////////////////////////////
+// English (United States) resources
+
+#if !defined(AFX_RESOURCE_DLL) || defined(AFX_TARG_ENU)
+LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US
+
+#ifdef APSTUDIO_INVOKED
+/////////////////////////////////////////////////////////////////////////////
+//
+// TEXTINCLUDE
+//
+
+1 TEXTINCLUDE
+BEGIN
+    "resource.h\0"
+END
+
+2 TEXTINCLUDE
+BEGIN
+    "#include ""winres.h""\r\n"
+    "\0"
+END
+
+3 TEXTINCLUDE
+BEGIN
+    "\r\n"
+    "\0"
+END
+
+#endif    // APSTUDIO_INVOKED
+
+
+/////////////////////////////////////////////////////////////////////////////
+//
+// Icon
+//
+
+// Icon with lowest ID value placed first to ensure application icon
+// remains consistent on all systems.
+IDI_APP_ICON            ICON                    "resources\\app_icon.ico"
+
+
+/////////////////////////////////////////////////////////////////////////////
+//
+// Version
+//
+
+#if defined(FLUTTER_VERSION_MAJOR) && defined(FLUTTER_VERSION_MINOR) && defined(FLUTTER_VERSION_PATCH) && defined(FLUTTER_VERSION_BUILD)
+#define VERSION_AS_NUMBER FLUTTER_VERSION_MAJOR,FLUTTER_VERSION_MINOR,FLUTTER_VERSION_PATCH,FLUTTER_VERSION_BUILD
+#else
+#define VERSION_AS_NUMBER 1,0,0,0
+#endif
+
+#if defined(FLUTTER_VERSION)
+#define VERSION_AS_STRING FLUTTER_VERSION
+#else
+#define VERSION_AS_STRING "1.0.0"
+#endif
+
+VS_VERSION_INFO VERSIONINFO
+ FILEVERSION VERSION_AS_NUMBER
+ PRODUCTVERSION VERSION_AS_NUMBER
+ FILEFLAGSMASK VS_FFI_FILEFLAGSMASK
+#ifdef _DEBUG
+ FILEFLAGS VS_FF_DEBUG
+#else
+ FILEFLAGS 0x0L
+#endif
+ FILEOS VOS__WINDOWS32
+ FILETYPE VFT_APP
+ FILESUBTYPE 0x0L
+BEGIN
+    BLOCK "StringFileInfo"
+    BEGIN
+        BLOCK "040904e4"
+        BEGIN
+            VALUE "CompanyName", "com.example" "\0"
+            VALUE "FileDescription", "flutter_rust_bridge_hello" "\0"
+            VALUE "FileVersion", VERSION_AS_STRING "\0"
+            VALUE "InternalName", "flutter_rust_bridge_hello" "\0"
+            VALUE "LegalCopyright", "Copyright (C) 2026 com.example. All rights reserved." "\0"
+            VALUE "OriginalFilename", "flutter_rust_bridge_hello.exe" "\0"
+            VALUE "ProductName", "flutter_rust_bridge_hello" "\0"
+            VALUE "ProductVersion", VERSION_AS_STRING "\0"
+        END
+    END
+    BLOCK "VarFileInfo"
+    BEGIN
+        VALUE "Translation", 0x409, 1252
+    END
+END
+
+#endif    // English (United States) resources
+/////////////////////////////////////////////////////////////////////////////
+
+
+
+#ifndef APSTUDIO_INVOKED
+/////////////////////////////////////////////////////////////////////////////
+//
+// Generated from the TEXTINCLUDE 3 resource.
+//
+
+
+/////////////////////////////////////////////////////////////////////////////
+#endif    // not APSTUDIO_INVOKED