Call the app by its name in every sentence that names it (#406)

APP_NAME renames an instance, but only the sign-in page, the title bar and
a few headings used it. Two dozen sentences wrote "ihasmail" into
themselves, so a renamed instance still told people to keep an ihasmail
tab open and offered to open mail links "in ihasmail".

Those sentences now take the name as {app}, which also lets a translator
put it where their language wants it. brand.ts grew useAppName() for
components and currentAppName() for the few places that build strings
outside React.

Left as they are: the Files folder "ihasmail", the Sieve script
"ihasmail" and ihasmail.org. Those name things a person can go and look
at, and renaming them would rename real data.

All nine catalogues keep their translations: the name inside each one
became the placeholder. Three of the strings had no translation before
and still fall back to English.

A test walks the sources and the catalogues so a new sentence can't
hard-code the name again.

web/src/lib/i18n.ts

@@ -120,7 +120,7 @@ export function plural(n: number, forms: PluralForms, vars?: Vars): string {
  *
  * So the sentence stays whole and the elements are placeholders in it:
  *
- *   tNode("Open {scheme} links in ihasmail.", { scheme: <code>mailto:</code> })
+ *   tNode("Open {scheme} links in {app}.", { scheme: <code>mailto:</code> }, { app: "ihasmail" })
  *
  * A translator sees one sentence with a named hole and can put the hole
  * wherever their language wants it.