deps: bump isocline to 41bb0c5

An agent REPL whose terminal went away kept running. Killing the tmux
session it ran in, or dropping the ssh connection, left read() returning
0 on stdin while select() kept reporting it readable, and isocline
treated that as "no key yet": the editor redrew and read again in a tight
loop, allocating each time. Two of them left behind by a screencast had
grown past 4 GiB each within minutes.

isocline now ends the edit on EOF or a read error, as Ctrl-D on an empty
line does, so the REPL quits. Its signal handler also stops swallowing
termination signals it has no previous handler to chain to, which is
what let the SIGHUP from that hangup go unnoticed.

SIGTERM in the REPL still behaves like Ctrl-C: that is Sighandler's
no_hard_exit, and isocline never sees it.

build.zig.zon

@@ -44,8 +44,8 @@
             .hash = "zenai-0.0.0-iOY_VAJHCQBfwIoPimnpcHayNdwoN8gHtUkr6ui5lMi0",
         },
         .isocline = .{
-            .url = "git+https://github.com/arrufat/isocline#4a99434bee4a5ed04c1639514224d48cd55e1405",
-            .hash = "N-V-__8AAHxtEwB16xj2Xz-zx_uklGdTP5C2-GHXDoSzah-8",
+            .url = "git+https://github.com/arrufat/isocline#41bb0c5380950b90440e74215c3e0e4821b8bbce",
+            .hash = "N-V-__8AAJVvEwAkVMvqVhi4hrCdFIzrefNcsl_OrnW1q_E4",
         },
         .pcre2 = .{
             .url = "git+https://github.com/PCRE2Project/pcre2#9ad4a2e956876747a5022bf04614c7e39e71d4ec",