build: exact per-binary imports — the pre-wired default set is gone

Every binary's build.zig now names precisely the modules its source
imports (derived by scanning each artifact's sources, transitively
through same-directory files), and its zon carries only the domains
those come from — kernel stays implicit (the root shim + link script
live there). build-support's userBinary resolves each name through one
module-to-domain table (module_homes); Domains/domains()/defaultImports
and the raw recipe entry point are deleted. An undeclared @import is a
compile error (verified: injecting @import("xkeyboard-config") into
logger fails with 'no module named ... available within module
program'), and e.g. xkeyboard-config now appears in exactly two
manifests — the two keyboard drivers. Availability never bloated the
emitted binaries (Zig compiles only what a program imports); this makes
the declared interfaces honest. Production and -Dtest-case manifests
byte-identical; all build variants and standalone package builds
green.

test/system/services/shared-memory-client/build.zig

@@ -1,7 +1,6 @@
-//! The shared-memory-client test fixture as a binary package (docs/build-packages-plan.md,
-//! phase 2): this file names only what is specific to this binary — the shared
-//! recipe and the default-import wiring live in build-support. The root build
-//! consumes the artifact(s) for the boot image.
+//! The shared-memory-client test fixture as a binary package (docs/build-packages-plan.md):
+//! this file names the binary and EXACTLY the modules its source imports —
+//! the shared recipe and the module-to-domain map live in build-support.
 
 const std = @import("std");
 const build_support = @import("build-support");
@@ -10,7 +9,7 @@ pub fn build(b: *std.Build) void {
     const exe = build_support.userBinary(b, .{
         .name = "shared-memory-client",
         .root_source_file = b.path("shared-memory-client.zig"),
-        .domains = build_support.domains(b),
+        .imports = &.{ "ipc", "logging", "memory", "time" },
     });
     b.installArtifact(exe);
 }

test/system/services/shared-memory-client/build.zig.zon

@@ -4,11 +4,11 @@
     .fingerprint = 0xc3945d0308ff5720, // Changing this has security and trust implications.
     .minimum_zig_version = "0.16.0",
     .dependencies = .{
+        // build-support supplies the shared recipe; kernel is implicit in
+        // every binary (the root shim + link script live there). The rest
+        // are exactly the homes of this binary's declared imports.
         .@"build-support" = .{ .path = "../../../../build-support" },
         .kernel = .{ .path = "../../../../library/kernel" },
-        .device = .{ .path = "../../../../library/device" },
-        .client = .{ .path = "../../../../library/client" },
-        .@"xkeyboard-config" = .{ .path = "../../../../library/xkeyboard-config" },
     },
     .paths = .{""},
 }