runtime: std.log for every user binary — kernel-stamped attribution

library/runtime/log.zig wires std.log to the tagged ring: the root shim
installs std_options for every binary (programs may override), logFn
formats one line per record and emits it with its level via
debug_write — the payload no longer carries the process's name; the
kernel stamps identity structurally and the serial renderer prints the
'<binary path>: ' prefix, so the transcript keeps its shape.

Migrate every writeLine/logLine/log helper family (init, vfs, fat,
device-manager, acpi, pci-bus, ps2-bus x3, usb-hid x2, usb-storage,
usb-xhci-bus, virtio-gpu — 104 call sites) to std.log.info, dropping
the hand-written prefixes. A leveled record is a complete line by
contract (raw emissions may still build lines from pieces). Test
fixtures and the display/input services keep raw writes for now — their
ring records are attributed by the kernel regardless.

Harness regexes follow the renamed prefixes (usb-hid-keyboard,
discovery) and path-named restart lines.

system/drivers/pci-bus/pci-bus.zig

@@ -16,11 +16,6 @@ const protocol = runtime.device_manager_protocol;
 const device = runtime.device;
 const pci_class = @import("pci-class");
 
-fn writeLine(comptime fmt: []const u8, arguments: anytype) void {
-    var line: [128]u8 = undefined;
-    _ = runtime.system.write(std.fmt.bufPrint(&line, fmt, arguments) catch return);
-}
-
 /// Log a discovered function with its (class / subclass / prog-IF) triple decoded
 /// to human names — the boot-log breadcrumb that says *what* the hardware is, so
 /// "class 0x01 (Mass Storage Controller) subclass 0x06 (Serial ATA Controller)
@@ -74,7 +69,7 @@ fn configWrite16(bus: u64, dev: u64, function: u64, offset: u64, value: u16) voi
 fn initialise(endpoint: runtime.ipc.Handle) bool {
     _ = endpoint;
     if (!device.claim(bridge_id)) {
-        writeLine("/system/drivers/pci-bus: unable to claim bridge device {d}\n", .{bridge_id});
+        std.log.info("unable to claim bridge device {d}", .{bridge_id});
         return false;
     }
     const buffer = runtime.allocator().alloc(device.DeviceDescriptor, 64) catch {
@@ -85,7 +80,7 @@ fn initialise(endpoint: runtime.ipc.Handle) bool {
     const descriptor = for (buffer[0..@min(total, buffer.len)]) |d| {
         if (d.id == bridge_id) break d;
     } else {
-        writeLine("/system/drivers/pci-bus: device {d} not in the device tree\n", .{bridge_id});
+        std.log.info("device {d} not in the device tree", .{bridge_id});
         return false;
     };
     // Resource 0 is the ECAM window (1 MiB of config space per bus); the bus
@@ -159,7 +154,7 @@ fn scan() void {
             }
         }
     }
-    writeLine("/system/drivers/pci-bus: {d} functions found\n", .{found});
+    std.log.info("{d} functions found", .{found});
 }
 
 /// Register one function under the bridge and report it to the manager. The
@@ -229,7 +224,7 @@ fn registerAndReport(bus: u64, dev: u64, function: u64, class_triple: u32) void
     }
 
     const registered = device.register(bridge_id, &descriptor) orelse {
-        writeLine("/system/drivers/pci-bus: register refused for {d}:{d}.{d}\n", .{ bus, dev, function });
+        std.log.info("register refused for {d}:{d}.{d}", .{ bus, dev, function });
         return;
     };
     const report = protocol.ChildAdded{
@@ -240,7 +235,7 @@ fn registerAndReport(bus: u64, dev: u64, function: u64, class_triple: u32) void
     };
     var reply: [protocol.message_maximum]u8 = undefined;
     _ = runtime.ipc.call(manager_handle, std.mem.asBytes(&report), &reply) catch {
-        writeLine("/system/drivers/pci-bus: child report for {d}:{d}.{d} failed\n", .{ bus, dev, function });
+        std.log.info("child report for {d}:{d}.{d} failed", .{ bus, dev, function });
     };
 }
 
@@ -255,7 +250,7 @@ fn onMessage(message: []const u8, reply: []u8, sender: u32, capability: ?runtime
 pub fn main(init: runtime.process.Init) void {
     const argument = init.arguments.get(1) orelse return; // bare (ramdisk sweep): stay silent
     bridge_id = std.fmt.parseInt(u64, argument, 10) catch {
-        writeLine("/system/drivers/pci-bus: malformed bridge device id '{s}'\n", .{argument});
+        std.log.info("malformed bridge device id '{s}'", .{argument});
         return;
     };
     runtime.service.run(protocol.message_maximum, .{