Find circuits by any id when topology is unavailable, and show unknown readings as unknown

[cayossarian]

Two fixes.

When the integration cannot report the panel's layout, the card still finds every circuit from its power sensor. That fallback reads the
entity registry, and took a circuit only from a unique id with a long hex segment. It now takes one circuit from each circuit power sensor. The
circuit id is everything between span_{serial}_ (the serial lower-cased, as the integration writes it) and the _power suffix, _ included.
A circuit whose power sensor is disabled is no longer found through its energy or current sensors, which before also made one of them its
"power" entity.

A reading the panel has not published shows as "--", never 0. An unknown or unavailable state read as 0, so the card drew 0 W, 0 A
and 0 % and added the term to sums. One helper, readNumber, now reads a state as a number or null:

• a null reading shows as "--", is not styled as production, and sorts after every measured circuit in the list;
• a circuit whose current has no reading draws no utilization, even when the current monitor still holds a figure;
• the header's sum of the circuits leaves out an unknown term and marks itself partial (stat-partial);
• every header reading starts unknown rather than 0;
• MonitoringPointInfo.utilization_pct is typed number | null, as the integration sends it.

A published 0 stays a reading.

The last commit rebuilds dist/.

Checks

• npm test: 561 passed in 56 files (520 in 53 before)
• npm run typecheck, npm run lint, node scripts/validate-i18n.mjs: clean
• npm run build: clean
• pre-commit hooks (prettier, eslint, typecheck, markdownlint, i18n) passed on every commit