Goal creation with pending retries, calendar task links, session-goal linking

[geokoko]

Summary

• In StudyPlanner panel, creating new Goals for a Task is not allowed if there are missed ones #31 — In the Study Planner, the "+ Create Goal" button now always renders in an expanded task card, even when the task only has missed goals waiting for a retry (previously the retry section replaced it entirely)
• Planning Goals for future days does not allow linking them with any tasks #30 — The Calendar's "Plan ahead for this day" dialog gains an optional "Link to task" selector (same pattern as the planner's add-goal dialog) and passes the selection through to addStudyGoal(desc, date, taskId)
• Link Study Session to Specific StudyGoal or Task #17 — Study sessions can be linked to a goal or task: new nullable goal_id/task_id columns on study_sessions (FKs added via named idempotent ALTER ... ADD CONSTRAINT IF NOT EXISTS, ON DELETE SET NULL), a startStudySession(goalId, taskId) overload, a "Link to (optional)" ComboBox next to Start Session listing today's open goals then uncovered tasks, and a muted link label on completed/incomplete session cards

Notes

• Based on Move missed-goal retry into task planner #29 (feature/planner-task-retry-controls) since all three fixes touch the attempt-based goal code introduced there; merge Move missed-goal retry into task planner #29 first, then retarget or merge this
• Not implemented (out of scope per Planning Goals for future days does not allow linking them with any tasks #30's "or create new ones on the fly"): creating a task from inside the calendar goal dialog

Test plan

• ./gradlew compileJava test (all green, includes new startStudySessionPersistsOptionalGoalAndTaskLink round-trip test)
• schema.sql executed twice against a fresh H2 database — idempotent, both FKs created exactly once

🤖 Generated with Claude Code