Replace raw state integers with named enum scopes in jobs

[JuanVqz]

Problem

Both DailyPuzzleJob and PuzzleInventoryCheckJob queried for approved puzzles using the raw integer state: 0 instead of the named enum scope:

# Fragile — breaks silently if enum values change
Puzzle.where(sent_at: nil, state: 0)
Puzzle.where(state: 0, sent_at: nil)

The integer 0 maps to approved today per the enum definition, but this is implicit and will silently return wrong results if the enum ever changes.

Fix

Puzzle.approved.where(sent_at: nil)

Tests

Added test files for both jobs (neither had any tests):

DailyPuzzleJobTest

• Only selects approved puzzles, not pending or rejected
• Only selects puzzles that have not been sent yet
• Marks the selected puzzle as archived and sets sent_at
• Does nothing when no approved unsent puzzles exist

PuzzleInventoryCheckJobTest

• Sends notification when fewer than 5 approved unsent puzzles exist
• Does not send notification when 5 or more approved unsent puzzles exist
• Only counts approved puzzles, not pending or rejected
• Only counts unsent puzzles

[JuanVqz]

nil guard does not fix the issue but discarding factors.