Detect and penalize ghost courses as missing in SPA solver

[google-labs-jules]

This change addresses an issue where courses with invalid time data (e.g., "Free Time" or unparsable time bitmaps) were silently ignored by the scheduler, leading to incomplete schedules without any warning or penalty.

Key changes in dist/static/js/solver.js:

1. Strict Candidate Filtering: Introduced isValidCandidate to explicitly reject candidates that have "自由时间" (Free Time) in their location text or whose schedule bitmaps parse to zero (i.e., no valid time slots).
2. Robust Missing Course Detection: Modified generateSchedules to capture the set of all course names the user intended to schedule (allRequiredNames) before any filtering occurs. The "missing course" check now compares the final schedule against this comprehensive list, ensuring that even if a group is completely filtered out (becoming empty/ghost), it is correctly identified as missing.
3. Increased Penalty: Increased the score penalty for missing courses from 10.0 to 500.0. This ensures that schedules with missing courses (including these ghost courses) are ranked significantly lower than complete schedules, matching user expectations.

Verified with a Node.js unit test and a Playwright frontend test (mocking the API to return ghost courses).

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PR created automatically by Jules for task 5984943680112991797 started by @OsakaLOOP

[google-labs-jules]

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