gather kernel tunables into config.zig

max_cpus, max_tasks, kernel/IST stack sizes, and timer_hz move from scattered constants into one config module. root.zig goes back to being just the boot contract. Values unchanged; any can become a -D build option later.

build.zig

@@ -61,6 +61,13 @@ pub fn build(b: *std.Build) void {
         .root_source_file = b.path("src/root.zig"),
     });
 
+    // Kernel tunables (max_cpus, stack sizes, tick rate). A dependency-free module of
+    // compile-time constants, imported wherever a knob is read; keeps the trade-offs
+    // in one place instead of scattered across the tree. See src/config.zig.
+    const config_mod = b.addModule("config", .{
+        .root_source_file = b.path("src/config.zig"),
+    });
+
     // Architecture-specific kernel code (CPU ops, entry, later GDT/IDT/paging).
     // The generic kernel imports this as "arch" and never names x86_64, so a new
     // architecture is a matter of pointing this module at a different directory.
@@ -68,6 +75,7 @@ pub fn build(b: *std.Build) void {
         .root_source_file = b.path("src/kernel/arch/x86_64/cpu.zig"),
         .imports = &.{
             .{ .name = "danos", .module = mod }, // paging uses the shared BootInfo/memory-map types
+            .{ .name = "config", .module = config_mod }, // max_cpus, ist_stack_size, timer_hz
         },
     });
     // CPU-exception stubs — real assembly, since they need cross-symbol
@@ -86,6 +94,7 @@ pub fn build(b: *std.Build) void {
         .root_source_file = b.path("src/device/platform.zig"),
         .imports = &.{
             .{ .name = "danos", .module = mod }, // BootInfo (carries the ACPI RSDP)
+            .{ .name = "config", .module = config_mod }, // max_cpus (the discovery pool)
         },
     });
 
@@ -122,6 +131,7 @@ pub fn build(b: *std.Build) void {
                 .{ .name = "danos", .module = mod },
                 .{ .name = "arch", .module = arch_mod },
                 .{ .name = "platform", .module = platform_mod },
+                .{ .name = "config", .module = config_mod },
                 .{ .name = "build_options", .module = build_options_mod },
             },
         }),