feat: add PostgreSQL events table with analytics indexes

- Add migration 001_create_events_table.sql with events table schema
- Add composite index on (group_id, event_type, created_at) for cycle analytics
- Add composite index on (member_address, event_type) for member history
- Add EXPLAIN ANALYZE benchmark script to measure query performance
- Add database README with usage instructions

Closes #[Performance] Add database query indexing for analytics

Author: Mirabliss

database/README.md

@@ -0,0 +1,29 @@
+# Database
+
+Off-chain PostgreSQL layer for indexing Soroban contract events to power the analytics dashboard.
+
+## Structure
+
+```
+database/
+├── migrations/
+│   └── 001_create_events_table.sql   # events table + analytics indexes
+└── benchmarks/
+    └── explain_analyze_indexes.sql   # EXPLAIN ANALYZE before/after comparison
+```
+
+## Applying the migration
+
+```bash
+psql -U <user> -d <dbname> -f database/migrations/001_create_events_table.sql
+```
+
+## Running benchmarks
+
+Seed the table first (see the seed helper comment in the benchmark file), then:
+
+```bash
+psql -U <user> -d <dbname> -f database/benchmarks/explain_analyze_indexes.sql
+```
+
+Compare `Planning Time` and `Execution Time` in the output before and after the migration.

database/benchmarks/explain_analyze_indexes.sql

@@ -0,0 +1,70 @@
+-- explain_analyze_indexes.sql
+-- Measures query execution time before and after adding the analytics indexes.
+--
+-- Usage:
+--   1. Run the BEFORE blocks BEFORE applying the migration (drop indexes if needed).
+--   2. Apply 001_create_events_table.sql
+--   3. Run the AFTER blocks and compare Planning/Execution times.
+--
+-- Requires: a populated `events` table with representative data.
+-- Tip: seed with at least 100k rows for meaningful results.
+
+-- ─── Seed helper (optional) ───────────────────────────────────────────────────
+-- INSERT INTO events (group_id, member_address, event_type, amount, cycle,
+--                     ledger_sequence, transaction_hash, created_at)
+-- SELECT
+--     (random() * 999 + 1)::BIGINT,
+--     'G' || substr(md5(random()::text), 1, 55),
+--     (ARRAY['ContributionMade','PayoutExecuted','MemberJoined','GroupCreated'])[ceil(random()*4)::int],
+--     (random() * 10000)::NUMERIC(20,7),
+--     (random() * 11 + 1)::INTEGER,
+--     (random() * 1000000)::BIGINT,
+--     md5(random()::text),
+--     NOW() - (random() * INTERVAL '365 days')
+-- FROM generate_series(1, 100000);
+
+-- ─────────────────────────────────────────────────────────────────────────────
+-- QUERY 1: Cycle analytics  (group_id, event_type, created_at)
+-- ─────────────────────────────────────────────────────────────────────────────
+
+-- BEFORE (sequential scan expected without index)
+EXPLAIN ANALYZE
+SELECT group_id, event_type, created_at, amount, cycle
+FROM   events
+WHERE  group_id   = 42
+  AND  event_type = 'ContributionMade'
+  AND  created_at >= NOW() - INTERVAL '30 days'
+ORDER BY created_at DESC;
+
+-- AFTER (index scan expected on idx_events_cycle_analytics)
+-- Run the same query again after migration — output should show:
+--   "Index Scan using idx_events_cycle_analytics on events"
+EXPLAIN ANALYZE
+SELECT group_id, event_type, created_at, amount, cycle
+FROM   events
+WHERE  group_id   = 42
+  AND  event_type = 'ContributionMade'
+  AND  created_at >= NOW() - INTERVAL '30 days'
+ORDER BY created_at DESC;
+
+-- ─────────────────────────────────────────────────────────────────────────────
+-- QUERY 2: Member history  (member_address, event_type)
+-- ─────────────────────────────────────────────────────────────────────────────
+
+-- BEFORE (sequential scan expected without index)
+EXPLAIN ANALYZE
+SELECT member_address, event_type, created_at, amount, group_id
+FROM   events
+WHERE  member_address = 'GBBD47IF6LWK7P7MDEVSCWR7DPUWV3NY3DTQEVFL4NAT4AQH3ZLLFLA5'
+  AND  event_type     = 'PayoutExecuted'
+ORDER BY created_at DESC;
+
+-- AFTER (index scan expected on idx_events_member_history)
+-- Run the same query again after migration — output should show:
+--   "Index Scan using idx_events_member_history on events"
+EXPLAIN ANALYZE
+SELECT member_address, event_type, created_at, amount, group_id
+FROM   events
+WHERE  member_address = 'GBBD47IF6LWK7P7MDEVSCWR7DPUWV3NY3DTQEVFL4NAT4AQH3ZLLFLA5'
+  AND  event_type     = 'PayoutExecuted'
+ORDER BY created_at DESC;

database/migrations/001_create_events_table.sql

@@ -0,0 +1,36 @@
+-- Migration: 001_create_events_table.sql
+-- Creates the events table for off-chain indexing of Soroban contract events.
+-- This table powers the analytics dashboard and leaderboard queries.
+
+CREATE TABLE IF NOT EXISTS events (
+    id               BIGSERIAL PRIMARY KEY,
+    group_id         BIGINT        NOT NULL,
+    member_address   VARCHAR(56)   NOT NULL,  -- Stellar address (G... format, max 56 chars)
+    event_type       VARCHAR(64)   NOT NULL,  -- e.g. 'ContributionMade', 'PayoutExecuted'
+    amount           NUMERIC(20,7),           -- XLM amount in stroops / 10^7
+    cycle            INTEGER,
+    ledger_sequence  BIGINT        NOT NULL,
+    transaction_hash VARCHAR(64)   NOT NULL,
+    created_at       TIMESTAMPTZ   NOT NULL DEFAULT NOW(),
+    raw_payload      JSONB                    -- full event payload for flexibility
+);
+
+-- ─── Indexes ──────────────────────────────────────────────────────────────────
+
+-- Index 1: Cycle analytics queries
+-- Supports dashboard queries that filter by group, event type, and time range.
+-- e.g. "show all ContributionMade events for group 42 in the last 30 days"
+CREATE INDEX IF NOT EXISTS idx_events_cycle_analytics
+    ON events (group_id, event_type, created_at DESC);
+
+-- Index 2: Member history queries
+-- Supports per-member history lookups filtered by event type.
+-- e.g. "show all PayoutExecuted events for member G...XYZ"
+CREATE INDEX IF NOT EXISTS idx_events_member_history
+    ON events (member_address, event_type);
+
+-- ─── Comments ─────────────────────────────────────────────────────────────────
+
+COMMENT ON TABLE  events                          IS 'Off-chain index of Soroban contract events for analytics.';
+COMMENT ON INDEX  idx_events_cycle_analytics      IS 'Speeds up cycle analytics dashboard queries (group_id, event_type, created_at).';
+COMMENT ON INDEX  idx_events_member_history       IS 'Speeds up member history queries (member_address, event_type).';