feat: implement comprehensive course data model with reference cache and search

migrations/20260128000000_expand_course_schema.sql

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+-- ============================================================
+-- Expand courses table with rich Banner API fields
+-- ============================================================
+
+-- Section identifiers
+ALTER TABLE courses ADD COLUMN sequence_number VARCHAR;
+ALTER TABLE courses ADD COLUMN part_of_term VARCHAR;
+
+-- Schedule & delivery (store codes, descriptions come from reference_data)
+ALTER TABLE courses ADD COLUMN instructional_method VARCHAR;
+ALTER TABLE courses ADD COLUMN campus VARCHAR;
+
+-- Credit hours
+ALTER TABLE courses ADD COLUMN credit_hours INTEGER;
+ALTER TABLE courses ADD COLUMN credit_hour_low INTEGER;
+ALTER TABLE courses ADD COLUMN credit_hour_high INTEGER;
+
+-- Cross-listing
+ALTER TABLE courses ADD COLUMN cross_list VARCHAR;
+ALTER TABLE courses ADD COLUMN cross_list_capacity INTEGER;
+ALTER TABLE courses ADD COLUMN cross_list_count INTEGER;
+
+-- Section linking
+ALTER TABLE courses ADD COLUMN link_identifier VARCHAR;
+ALTER TABLE courses ADD COLUMN is_section_linked BOOLEAN;
+
+-- JSONB columns for 1-to-many data
+ALTER TABLE courses ADD COLUMN meeting_times JSONB NOT NULL DEFAULT '[]'::jsonb;
+ALTER TABLE courses ADD COLUMN attributes JSONB NOT NULL DEFAULT '[]'::jsonb;
+
+-- ============================================================
+-- Full-text search support
+-- ============================================================
+
+-- Generated tsvector for word-based search on title
+ALTER TABLE courses ADD COLUMN title_search tsvector
+    GENERATED ALWAYS AS (to_tsvector('simple', coalesce(title, ''))) STORED;
+
+CREATE INDEX idx_courses_title_search ON courses USING GIN (title_search);
+
+-- Trigram index for substring/ILIKE search on title
+CREATE EXTENSION IF NOT EXISTS pg_trgm;
+CREATE INDEX idx_courses_title_trgm ON courses USING GIN (title gin_trgm_ops);
+
+-- ============================================================
+-- New filter indexes
+-- ============================================================
+
+CREATE INDEX idx_courses_instructional_method ON courses(instructional_method);
+CREATE INDEX idx_courses_campus ON courses(campus);
+
+-- Composite for "open CS courses in Fall 2024" pattern
+CREATE INDEX idx_courses_term_subject_avail ON courses(term_code, subject, max_enrollment, enrollment);
+
+-- ============================================================
+-- Instructors table (normalized, deduplicated)
+-- ============================================================
+
+CREATE TABLE instructors (
+    banner_id VARCHAR PRIMARY KEY,
+    display_name VARCHAR NOT NULL,
+    email VARCHAR
+);
+
+CREATE TABLE course_instructors (
+    course_id INTEGER NOT NULL REFERENCES courses(id) ON DELETE CASCADE,
+    instructor_id VARCHAR NOT NULL REFERENCES instructors(banner_id) ON DELETE CASCADE,
+    is_primary BOOLEAN NOT NULL DEFAULT false,
+    PRIMARY KEY (course_id, instructor_id)
+);
+
+CREATE INDEX idx_course_instructors_instructor ON course_instructors(instructor_id);
+
+-- ============================================================
+-- Reference data table (all code→description lookups)
+-- ============================================================
+
+CREATE TABLE reference_data (
+    category VARCHAR NOT NULL,
+    code VARCHAR NOT NULL,
+    description VARCHAR NOT NULL,
+    PRIMARY KEY (category, code)
+);