M11–M12: IRQ-as-IPC and bus drivers; expand names tree-wide

Two driver-model milestones plus a tree-wide naming pass. Suite 35/35
(QEMU) + host tests green.

M11 — IRQ-as-IPC. A ring-3 driver now sleeps until its device interrupts
it. New src/kernel/irq.zig: per-GSI endpoint bindings, comptime per-vector
trampolines, dispatch = mask GSI -> LAPIC EOI -> notifyLocked, all under one
lock region. irq_bind/irq_ack syscalls, gated by the device claim like
mmio_map. interruptDispatch no longer EOIs — each handler owns its EOI,
because a level line must be masked before it is acknowledged (irq_ack is
the unmask). Bindings are keyed on the owning task and released on exit
(a shared endpoint's siblings survive). hpetd rewritten interrupt-driven.
Tests: hpet (rewritten, reads back the I/O APIC routing) and irqfree.

M12 — bus drivers. DeviceDesc gains a parent, making the device table a
tree. dev_register (device_register) lets a process publish children below
a device it claimed; the kernel enforces resource containment (a child's
resources must nest in its parent's), so a descriptor can't fabricate a
window over kernel RAM. Descriptor copied in via copyFromUser (physmap
walk — an unmapped user pointer fails the call instead of faulting the
kernel). Per-parent child cap bounds table exhaustion. sbin/busd.zig is a
worked bus driver. Test: bus.

Naming — per docs/coding-standards.md: non-acronym abbreviations spelled
out (message, descriptor, device_service, scheduler, runtime, physical,
interpreter, ...); acronyms kept (IPC, MMIO, DMA, HCD, ...); files are
kebab-case (ipc-synchronous.zig, device-service.zig, vfs-protocol.zig, ...).
Exceptions: POSIX/C ABI names and Zig idioms (init/len/ptr) kept. Module
collisions resolved by specific naming (config -> parameters, device.zig
alias -> device_model). AML op/Op disambiguated: op = opcode, Op =
operation; per-opcode parse handlers renamed opX -> parseX.

New driver docs: drivers.md, driver-model.md (bus/class/HCD shapes + the
proposed M13–M16 ABI), coding-standards.md.

lib/stdio.zig

@@ -8,7 +8,7 @@ const unistd = @import("unistd.zig");
 const heap = @import("heap.zig");
 
 pub const SEEK_SET = unistd.SEEK_SET;
-pub const SEEK_CUR = unistd.SEEK_CUR;
+pub const SEEK_CURRENT = unistd.SEEK_CURRENT;
 pub const SEEK_END = unistd.SEEK_END;
 
 /// A C `FILE`: an fd plus sticky end-of-file / error flags. Allocated on the
@@ -47,10 +47,10 @@ pub fn fclose(f: *FILE) c_int {
 }
 
 /// Read `size*nmemb` bytes; returns the number of whole items read.
-pub fn fread(buf: []u8, size: usize, nmemb: usize, f: *FILE) usize {
+pub fn fread(buffer: []u8, size: usize, nmemb: usize, f: *FILE) usize {
     const total = size * nmemb;
     if (total == 0) return 0;
-    const n = unistd.read(f.fd, buf[0..@min(buf.len, total)]);
+    const n = unistd.read(f.fd, buffer[0..@min(buffer.len, total)]);
     if (n <= 0) {
         f.eof = 1;
         return 0;
@@ -76,7 +76,7 @@ pub fn fseek(f: *FILE, off: i64, whence: u32) c_int {
 }
 
 pub fn ftell(f: *FILE) i64 {
-    return unistd.lseek(f.fd, 0, unistd.SEEK_CUR);
+    return unistd.lseek(f.fd, 0, unistd.SEEK_CURRENT);
 }
 
 pub fn rewind(f: *FILE) void {