Generalize BMS cell data model for arbitrary cell counts

[bracyw]

Description

The BMS data model hardcodes cell counts as fixed-length tuples and enums. This year's accumulator has a different cell configuration, and the UI needs to support any reasonable number of cells per segment without code changes. A single config should drive cell/segment counts across the entire data layer.

Acceptance Criteria

• Cell and segment counts are defined in one place and all data structures derive from them
• Adding or removing cells/segments only requires changing config values — no type or enum changes needed
• No change in behavior — all existing subscriptions, rendering, and tests continue to work

Proposed Solution

Introduce a BMS_CONFIG in bms.utils.ts, replace fixed tuple types and index enums with config-driven arrays throughout bms.utils.ts, topic.utils.ts, and cell.service.ts. No UI changes.