Step 1 (account selection) now tells the user to pick the "Other"
account if they're not sure. The Description field's placeholder is
rewritten to prompt for a detailed description of the purchase /
invoice / bill and what it was used for (event/project/etc), replacing
the redundant helper line.
Client feedback: with no fixed category taxonomy yet, steering unsure
users to the Other account plus a richer free-text description lets us
reconcile/recategorize later.
Refs aiolabs/webapp#137
