Extract Shared JS Utility Functions (utils.js)

[w2naf]

Description

Extract duplicated utility functions from map_ft.js and table_ft.js into a shared utils.js module.

Known Duplications

• Time parsing logic (YYMMDD + HHMM → Date) exists in both map and table JS files
• Maidenhead grid-to-lat/lon conversion may be duplicated
• Other common helpers

Acceptance Criteria

• utils.js created with shared utility functions
• Duplicated code removed from map_ft.js and table_ft.js
• Both views import and use the shared utilities
• No functional regressions

Milestone

Milestone 1: Minimal Working System (Feb 28)