Consolidate per-language data files for daily word selection

[Hugo0]

Problem

There are currently 3 overlapping mechanisms controlling daily word selection:

• _daily_words.txt — curated subset of words used as daily words
• _blocklist.txt — exclusion list to prevent certain words from appearing
• _curated_schedule.txt — day-by-day override for specific dates

Plus the fallback to _5words.txt (full word list) when no curated daily list exists.

Proposal

Unify these into a single curated daily word list per language. This would:

• Simplify the word selection logic in webapp/app.py
• Make it easier to audit what words will appear
• Remove edge cases where blocklist and curated schedule interact unexpectedly

Current code

See Language._get_daily_word() in webapp/app.py for the current selection logic.