The notification dropdown is anchored to the bell button, which on mobile sits
left of the account button rather than at the screen edge, so the wide panel
overflowed off the left of the viewport (title/text cut off). On narrow screens,
drop .notif's positioning context so the dropdown anchors to the .acct cluster at
the header's right edge, keeping it fully on-screen.
Also add route-level tests for the accounts feature (auth flow, subscription CRUD,
duplicate/validation, ownership 404s, notifications), plus a
THERMOGRAPH_ACCOUNTS_DB override so the suite writes to a throwaway DB and stays
hermetic.
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