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.
Hoist max_cpus into danos (root.zig), raise it to 128, and stop reserving a static [max_cpus][16 KiB] IST array. Only the BSP's IST stack is static (needed before the allocator); each AP's is heap-allocated when it comes online. Shrinks the kernel from ~1.1 MB to ~139 KiB in ReleaseSmall.