build: phase 2 wave A — services build as packages

init, fat, display, display-demo, device-manager, input, logger, and
the two discovery fillers (acpi, fdt — each exporting an artifact named
"discovery"; the root -Ddiscovery picks which ships) convert to binary
packages on the pci-bus template. init's serial heartbeat flag rides
the dependency options (the root forwards its -Dserial). fat's and
display's unit tests move into their packages and the root aggregate
delegates to them. Boot-image file list unchanged.

build.zig.zon

@@ -44,6 +44,15 @@
         .@"xkeyboard-config" = .{ .path = "library/xkeyboard-config" },
         // Binary packages (phase 2), consumed as artifacts for the boot image.
         .@"pci-bus" = .{ .path = "system/drivers/pci-bus" },
+        .init = .{ .path = "system/services/init" },
+        .fat = .{ .path = "system/services/fat" },
+        .display = .{ .path = "system/services/display" },
+        .@"display-demo" = .{ .path = "system/services/display-demo" },
+        .@"device-manager" = .{ .path = "system/services/device-manager" },
+        .input = .{ .path = "system/services/input" },
+        .logger = .{ .path = "system/services/logger" },
+        .acpi = .{ .path = "system/services/acpi" },
+        .fdt = .{ .path = "system/services/fdt" },
         // See `zig fetch --save <url>` for a command-line interface for adding dependencies.
         //.example = .{
         //    // When updating this field to a new URL, be sure to delete the corresponding