feat: export BASE environment variable for vite and vite-plus actions

[torn4dom4n]

This change exports the BASE environment variable for both vite and vite-plus actions, in addition to VITE_SITE_URL. It also adds robust tests and workflows verification, and optimizes vite.config.ts pack configuration to prevent shared chunk generation.

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PR created automatically by Jules for task 7843915494332784722 started by @torn4dom4n

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