Allow dots in app names (closes #260)

App names may now contain dots, such as sneak.berlin: runs of
lowercase letters and numbers joined by single dots or by hyphens,
2 to 63 characters. Docker accepts every such name in the app's image
name, upaas-<name>; a dot needs a letter or number on both sides
because Docker requires it. The rule also keeps a dot off either end,
so the name is safe as a directory and log file name.

The new and edit app forms use the same pattern. Their old one was not
a valid regular expression under the flag browsers compile it with, so
browsers ignored it.

A test deploys an app named sneak.berlin against the fake Docker API
and checks the image and container names with Docker's own rules.

Model: opus-5-5

TODO.md

@@ -20,6 +20,13 @@ regress.
 
 # Completed Steps
 
+- 2026-10-02: App names may contain dots, such as `sneak.berlin`: lowercase
+  letters and numbers joined by single dots or by hyphens, 2 to 63 characters.
+  Docker accepts every such name in the image name `upaas-<name>`; a dot needs a
+  letter or number on both sides because Docker requires it. The new and edit
+  app forms check the same rule; browsers ignored their old pattern, which was
+  not a valid regular expression there (#260).
+
 - 2026-10-02: The build no longer passes the CPU architecture in: upaas reads it
   from Go's `runtime.GOARCH` when it runs, and the startup log line reports it
   as `arch`. `CONVENTIONS.md` follows the updated conventions in `sneak/prompts`