[chore] Add migration to reconcile stale plot_count data

[realproject7]

Context

PR #258 fixed the code path — plot_count and last_plot_time now reconcile on every plot index and backfill. But existing storylines still have stale data from before the fix (e.g., storylines showing plot_count=1 despite having 3+ plots chained).

Task

Add a Supabase migration that reconciles all existing storylines.plot_count and last_plot_time from the plots table.

Migration SQL

UPDATE storylines s
SET plot_count = sub.cnt,
    last_plot_time = sub.latest
FROM (
  SELECT storyline_id,
         COUNT(*) AS cnt,
         MAX(block_timestamp) AS latest
  FROM plots
  GROUP BY storyline_id
) sub
WHERE s.storyline_id = sub.storyline_id
  AND (s.plot_count != sub.cnt OR s.last_plot_time != sub.latest);

File

Create supabase/migrations/00009_reconcile_plot_counts.sql (check the latest migration number and increment).

Acceptance criteria

• Migration file created with the reconciliation SQL
• npm run typecheck passes
• Idempotent — running the migration twice produces the same result