Add lessons Phase 4: lesson sessions with hybrid calendar generation

Individual lesson occurrences generated from schedule slot patterns.
Idempotent session generation with configurable rolling window.
Post-lesson notes workflow with auto-set notesCompletedAt. Status
tracking (scheduled/attended/missed/makeup/cancelled) and date/time
filtering. 13 new tests (64 total lessons tests).

packages/backend/src/db/migrations/0031_lesson_sessions.sql

@@ -0,0 +1,22 @@
+-- Phase 4: Lesson sessions — individual lesson occurrences
+
+CREATE TYPE "lesson_session_status" AS ENUM ('scheduled', 'attended', 'missed', 'makeup', 'cancelled');
+
+CREATE TABLE "lesson_session" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  "enrollment_id" uuid NOT NULL REFERENCES "enrollment"("id"),
+  "scheduled_date" date NOT NULL,
+  "scheduled_time" time NOT NULL,
+  "actual_start_time" time,
+  "actual_end_time" time,
+  "status" lesson_session_status NOT NULL DEFAULT 'scheduled',
+  "instructor_notes" text,
+  "member_notes" text,
+  "homework_assigned" text,
+  "next_lesson_goals" text,
+  "topics_covered" text[],
+  "makeup_for_session_id" uuid,
+  "notes_completed_at" timestamptz,
+  "created_at" timestamptz NOT NULL DEFAULT now(),
+  "updated_at" timestamptz NOT NULL DEFAULT now()
+);

packages/backend/src/db/migrations/meta/_journal.json

@@ -218,6 +218,13 @@
       "when": 1774900000000,
       "tag": "0030_enrollments",
       "breakpoints": true
+    },
+    {
+      "idx": 31,
+      "version": "7",
+      "when": 1774910000000,
+      "tag": "0031_lesson_sessions",
+      "breakpoints": true
     }
   ]
 }