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/kernel/log.zig

@@ -118,10 +118,12 @@ fn appendLocked(pid: u32, name: []const u8, level: abi.KlogLevel, now: u64, byte
     var rest = bytes;
     while (rest.len != 0) {
         const newline = std.mem.indexOfScalar(u8, rest, '\n');
-        // The record payload excludes the newline: a record IS a line (or the
-        // open tail of one when the emission didn't end in '\n').
+        // The record payload excludes the newline: a record IS a line. Raw
+        // emissions may leave a line open (kernel boot tables build lines from
+        // pieces); a LEVELED record is a complete line by contract — std.log
+        // payloads carry no trailing newline.
         const line = if (newline) |i| rest[0..i] else rest;
-        const line_complete = newline != null;
+        const line_complete = newline != null or level != .raw;
         if (line.len != 0 or line_complete)
             _ = ring.append(pid, name, level, now, line, line.len > abi.klog_maximum_message);
         render(pid, name, level, line, line_complete);