check_cards: an extra card figure is accepted, and a card with an unreadable figure is reported as missing

[realmarcin]

From the round-1 review of #212 (#114).

Where: scripts/fleet/card_markup.py:29, scripts/fleet/assemble_page.py:119, scripts/fleet/check_cards.py:199-200.

Extra figures pass. card_figures() keeps only the first <div class="num"><b>N</b> inside each <article> and ignores any others, and any figure outside every card. At 8e49cd0, all three of these failed with "Every Mech card must carry a record count". On the branch they all pass:

• a second stat tile above HabitatMech's headline, which renders the records tile as 1,072,961 instead of 1,075,481;
• a second tile after the headline;
• a stray figure outside the cards.

Unreadable figures get the wrong message. A card whose figure doesn't parse (for example <b>625,960 </b>) drops out of card_figures(). check_cards.py then reports "UNCARDED TaxonMech: SOURCES entry with no card in the template" and advises adding a missing card. The card exists; only its figure markup is wrong.

Fix: have card_markup report every figure per card and any figure outside a card. assemble_page then requires exactly one figure per card, and check_cards reports a card with no figure or with several as a markup failure, not as UNCARDED.