Matrix bridge scaffold: test harness with texting E2E

- src/matrix.zig: minimal Matrix client (conduwuit @ matrix.chaosmith.systems)
  via curl subprocess transport (native TLS swap later): login, createRoom
  (trusted_private_chat, unencrypted — no olm), sendText, sync polling with
  window-scan event extraction reusing letta.jsonStr
- src/matrix_harness.zig: standalone entrypoint (independent of tray daemon):
  login -> DM with peer -> sync loop -> peer messages routed through letta
  CLI (chaos-prime) -> replies sent back to the room
- build.zig: second exe matrix_harness; use_llvm fix promoted into build.zig
  for both executables (native lld vs GCC16 .sframe relocations)
- calling/Element Call (livekit SFU already deployed on ass-host) layers on
  top of this harness next

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta Code <noreply@letta.com>

build.zig

@@ -58,8 +58,28 @@ pub fn build(b: *std.Build) void {
 
     configureQtExeRootModule(b, exe, .{}) catch @panic("Qt configuration failed");
 
+    exe.use_llvm = true; // native lld chokes on GCC16 .sframe relocations
     b.installArtifact(exe);
 
+    // Matrix bridge test harness (independent of the tray daemon).
+    const harness = b.addExecutable(.{
+        .name = "matrix_harness",
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("src/matrix_harness.zig"),
+            .target = target,
+            .optimize = optimize,
+            .link_libc = true,
+            .imports = &.{
+                .{ .name = "libqt6zig", .module = qt6zig.module("libqt6zig") },
+            },
+        }),
+    });
+    for (qt_libraries) |lib|
+        harness.root_module.linkLibrary(qt6zig.artifact(lib));
+    configureQtExeRootModule(b, harness, .{}) catch @panic("Qt configuration failed");
+    harness.use_llvm = true;
+    b.installArtifact(harness);
+
     const run_step = b.step("run", "Run inferon");
     const run_cmd = b.addRunArtifact(exe);
     run_step.dependOn(&run_cmd.step);