/forges shows each sent forge's crew spend today against its starter budget, carried by its heartbeat #5866

For a forge in a link, the client list should say whether a client's crew is burning through what it was given. Today the heartbeat (src/spawn/heartbeat.ts) carries version, tip, proposals and upstream lag, but no spend.

Done when:

• [ ] The child's heartbeat adds spendTodayUsd and ceilingUsd, the forge cap or null. Both are validated on receipt like the other fields; a bad value drops the field, not the beat.
• [ ] Each row on /forges (src/web/pages/forges.ts) reads $3.20 of $10 today. It turns attention-toned at 80% and says ceiling reached at 100%. A child that has not reported spend shows nothing new.
• [ ] MCP forges gives the same two numbers per child.
• [ ] Tests: a beat with spend, one without, one with a negative or non-numeric value, and the row's words at 50%, 85% and 100%.