Fix full-capacity Worker slot display

[miiiinju1]

Description and motivation

#3833 fixed the total slot calculation to use available slots plus used slots. One edge case remained: a zero available-slot count failed the existing truthiness check, so a Worker at full capacity rendered as 3 instead of 3/3.

Worker slot counts are proto3 scalar fields. The UI Server JSON marshaler omits zero-valued scalars, so currentAvailableSlots can also arrive as undefined when its protobuf value is zero. This change restores the protobuf zero defaults before rendering, while keeping -1 as unknown capacity and preserving the empty state when slot data is absent or both counts are zero.

Screenshots

Not applicable. The rendered states are covered by component tests.

Design considerations

The fallback applies only to counts within the existing slot display. A missing slot record still renders the existing empty state.

Testing

Added unit coverage for:

• 0/3, 1/3, 2/3, and 3/3
• nullish available counts using the protobuf zero default
• the zero-slot empty state
• unknown availability with -1
• missing slot data

How was this tested

• Manual testing
• E2E tests added
• Unit tests added

Validation completed:

• pnpm exec vitest run src/lib/components/workers/worker-details/worker-details.svelte.test.ts: 9 tests passed
• pnpm test --run: 3,142 tests passed and 2 skipped
• pnpm lint:ci: passed with no errors
• pnpm check: passed with no errors

Steps for others to test

Run:

pnpm exec vitest run src/lib/components/workers/worker-details/worker-details.svelte.test.ts

Checklists

Draft checklist

Ready for review.

Merge checklist

No follow-up changes are required.

Issues closed

None.

Docs

Any docs updates needed?

No.

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