input: total keyboard routing + per-terminal discipline (ADR 0006 ph1)

wm: FOCUSED is now a plain window id — window 0 (home terminal) is an
ordinary focusable window in the z-order.  The CONSOLE sentinel
(usize::MAX) and the focused()==0 special cases are gone; focus_console()
is an alias for focus(0).  Desktop clicks focus window 0.  The WM input
pump routes every key unconditionally: IRQ ring -> pump -> focused
window's owner; nothing polls the scancode rings directly any more.

tty: read_line() reads from the calling task's message queue (the old
global-ring read_line and the duplicate read_line_from_queue are merged);
raw mode (read_byte/try_read_byte) consumes the same queue;
interrupt_pressed drains the queue instead of the ring.

shell: task 0 owns home terminal window 0 and blocks on its queue like a
windowed shell; cat/hexdump stdin paths pass the home terminal handle.

sched: watchdog comments updated (shell parks on recv_blocking).

Verified in QEMU: F1 spawns terminals, F2 cycles focus home->term1->
term2, keystrokes land only in the focused window, ^C cancels a line,
edit runs raw over the queue and exits to a working prompt; test-disk
regression PASS.

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