fix : added TTL-based cache invalidation to data_loader

[tmdeveloper007]

Summary of What Has Been Done

Added time-based cache expiration to load_all_projects() in src/utils/data_loader.py so the in-memory project cache does not serve stale data indefinitely.

Changes Made

• Added _projects_cache_time global to track when the cache was last populated
• Added _CACHE_TTL_SECONDS = 300 (5-minute TTL constant)
• Added _cache_expired() helper that returns True when the cache is missing or older than the TTL
• Updated load_all_projects() to use _cache_expired() instead of a bare None check, and to record time.time() on cache miss
• Updated clear_cache() to also reset _projects_cache_time to 0

Impact it Made

Users will always see project data that is at most 5 minutes old instead of potentially stale cached data from when the app started. This fixes a data consistency bug where database updates were invisible to running instances.

Note: Please assign this PR to the tmdeveloper007 account.

Closes #1318

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