kernel: the boot transcript on screen, every line timestamped

Without serial and without working USB storage, a slow real-hardware
boot is undiagnosable — 'stabbing in the dark'. Two changes end that:

The log renderer stamps every line with boot-relative seconds
([  12.045] ...), so every surface — serial, debugcon, and now the
screen — is a readable timeline. And the framebuffer console registers
as an ordinary log sink at boot: kernel AND userspace lines (device
bring-up, fat mounts, logger announcements) show live on screen until
the display service claims the framebuffer, which flips the console's
suppression and silences the sink automatically — the display-owns-the-
screen design is unchanged in normal operation; the console now simply
narrates the part of boot that happens before there IS a display.

On the machine that motivated this, the next boot will show by eye
where the minutes go — including whether the USB chain ever brings
storage up, and whether screen drawing itself crawls (the latent
non-write-combining framebuffer suspect: if these very lines paint
slowly, that's the answer).

system/kernel/kernel.zig

@@ -162,6 +162,13 @@ fn kmain(boot_information: *const BootInformation) noreturn {
     // uncached crawl). Routine boot output goes only to the log; this console now exists for
     // early-boot and fatal (`fatal`/panic) output, until the display service takes over.
     console.init(fb);
+    // The console joins the log sinks: the boot transcript — kernel AND
+    // userspace lines, each timestamped by the renderer — shows on screen
+    // until the display service claims the framebuffer (which flips the
+    // console's `suppressed` and silences this sink). On a machine with no
+    // serial this is the only live view of the boot, and a slow boot becomes
+    // diagnosable by eye: the timeline is right there.
+    if (console.present()) log.addSink(console.write);
     log.write(if (console.present())
         "/system/kernel: framebuffer ready (early-boot + fatal fallback; the display service drives it in normal operation)\n"
     else