docs: replace the screen catalogue with a real step-by-step tutorial

The previous PDF showed screens from the outside — long full-page dumps
of lists, with no instruction. This one teaches the system by driving
it: every step opens the screen, fills the form with real data, submits,
shows the result, and then shows the journal entry that operation
produced. Screenshots are top-of-screen crops only.

93 steps across 11 chapters: manual journal entry; the full fixed-asset
lifecycle (purchase, maintenance, monthly depreciation, disposal with
gain/loss) with the auto-generated entry after each; the government
procurement cycle from PR through tender, committees, technical
evaluation, the 3-offer gate, re-tender, award by item and the
resulting purchase orders; the auction cycle from lots and committees
through bidding, award, collection and the disposal entry; payment and
receipt vouchers with cheque tracking; asset custody; GL sync preview;
and the five financial statements.

The superseded catalogue PDF is removed — it remains in git history.