fix(mobile): hide non-positive DotCount values

[tallyhuhu]

Summary

DotCount documents that it should be hidden when count <= 0, but the mobile implementation only handled zero and could display negative values. This change aligns mobile behavior with the existing web implementation by hiding all non-positive counts while preserving enter and exit animations.

Added regression coverage for negative counts.

Testing

• yarn nx run mobile:test --testMatch='**/*.test.tsx' --testPathPattern=DotCount.test.tsx
• yarn nx run mobile:typecheck
• yarn nx format:write

[cb-heimdall]

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