fix: missing fall 2026 term in schedule dropdown

[jaspermayone]

Fixes #502

Root cause

The season enum stores non-chronological values (spring: 1, fall: 2, summer: 3), and Term.current_and_future compared seasons by raw enum value:

where("(year > ?) OR (year = ? AND season >= ?)", ...)

During a summer term (season value 3), fall of the same year (season value 2) fails the >= 3 check — so the Fall option disappears from the schedule dropdown every summer. The same raw values were used in order(season: ...) calls, sorting Fall before Summer within a year across the app.

Changes

• Added Term::SEASON_CHRONOLOGICAL_POSITIONS and a season_position_sql CASE expression that maps stored enum values to chronological order (spring → summer → fall). No data migration needed.
• New chronological / reverse_chronological scopes; replaced all raw order(year:, season:) usages (term scopes, admin terms/course catalog/finals schedules/rooms).
• current_and_future now compares by chronological position, so Fall 2026 shows during Summer 2026.
• The schedule page now only offers terms the user has enrollments in (new Term.enrolled_for(user) scope), and the selected term is resolved from that list rather than any term_uid param.

flowchart LR
    A[Term.enrolled_for user] --> B[current_and_future]
    B -->|empty| C[last 6 enrolled terms]
    B -->|present| D[term dropdown]
    C --> D

Loading

Tests

Model specs for the chronological scopes, current_and_future in both summer and fall, enrolled_for, and season_position. Full suite passes locally.