WS-B.4: scripts/file-budget.sh ratchet + CI wiring

[LukasWodka]

Part of epic tracebloc/backend#1106. Full spec: report §5 (mirrored on the epic; artifact https://claude.ai/code/artifact/b4b6e6a6-4d76-4e46-a668-6f4f0f944344). WS-B PR4: clone the coverage-floor.sh pattern — path:max_lines, ceilings ratchet DOWN only, raising = reviewed diff. Seeds: preflight.go:1650, data.go re-seed 500 post-split, client.go:1050, home.go:850. Wire into make ci + build.yml. Shell ratchet over golangci funlen per the #6 standalone-tools decision.

[LukasWodka]

Shipped in #316 (merged to develop). Closing as completed — CLI refactor epic backend#1106 cleanup.