fix: prevent Oban index bloat by reindexing primary key and scheduling index (#165)

Severe index bloat discovered on oban_jobs:
- oban_jobs_pkey: 82.2 bloat ratio, 3.2GB waste
- oban_jobs_state_queue_priority_scheduled_at_id_index: 216.8 bloat, 7.9GB waste

Root cause: High DELETE churn from aggressive Pruner config (10k jobs/sec)
causes PostgreSQL VACUUM to leave dead index entries. VACUUM only marks space
as reusable but cannot shrink indexes.

The Oban Reindexer plugin was only reindexing args_index and meta_index by
default, missing the primary key and main scheduling index.

Solution: Explicitly configure Reindexer to include all high-churn indexes:
- oban_jobs_pkey (primary key, used by all queries)
- oban_jobs_state_queue_priority_scheduled_at_id_index (job scheduling)
- oban_jobs_args_index (default, GIN index)
- oban_jobs_meta_index (default, GIN index)

Daily REINDEX CONCURRENTLY at 2 AM will prevent future bloat accumulation.

Manual immediate reindex required to reclaim 11GB:
  REINDEX INDEX CONCURRENTLY oban_jobs_pkey;
  REINDEX INDEX CONCURRENTLY oban_jobs_state_queue_priority_scheduled_at_id_index;

Reviewed-on: graham/towerops-web#165

config/runtime.exs

@@ -261,8 +261,19 @@ if config_env() == :prod do
       # causing oban_jobs to bloat to millions of rows and slow all queries.
       # 50k/5s (10,000/s) keeps the table small.
       {Oban.Plugins.Pruner, max_age: 60, limit: 50_000, interval: to_timeout(second: 5)},
-      # Rescue orphaned jobs (when node crashes)
-      {Oban.Plugins.Reindexer, schedule: "0 2 * * *"},
+      # Rescue orphaned jobs (when node crashes) and prevent index bloat
+      # High DELETE churn (10k jobs/sec pruned) causes severe index bloat on:
+      #   - Primary key (82.2 bloat, 3.2GB waste)
+      #   - Scheduling index (216.8 bloat, 7.9GB waste)
+      # REINDEX CONCURRENTLY reclaims space without blocking operations.
+      {Oban.Plugins.Reindexer,
+       schedule: "0 2 * * *",
+       indexes: [
+         "oban_jobs_pkey",
+         "oban_jobs_state_queue_priority_scheduled_at_id_index",
+         "oban_jobs_args_index",
+         "oban_jobs_meta_index"
+       ]},
       # Rescue jobs stuck in executing state (mark as cancelled after 10 minutes)
       {Oban.Plugins.Lifeline, rescue_after: to_timeout(minute: 10)}
     ]