docs: align partitioning strategy with LIST by chain_id

Update database schema documentation to use LIST partitioning by chain_id
instead of TimescaleDB time-based partitioning, aligning with the primary
nonce-based query pattern.

Changes:
- Replace partition examples with LIST by chain_id approach
- Add nonce-based indexes as primary access pattern
- Add time-based indexes as secondary (for export endpoint)
- Emphasize partition-specific indexes for high-volume chains

Author: gfendres

docs/phase-2-3/database-schema.md

@@ -765,19 +765,40 @@ CREATE INDEX idx_multisig_tx_safe_nonce ON multisig_transactions(chain_id, safe,
 CREATE INDEX idx_erc20_to_from ON erc20_transfers(chain_id, to_address, from_address);
 ```
 
-### 2. Partition Large Tables
+### 2. Partition Large Tables (LIST by chain_id)
 
 ```sql
--- Partition by chain_id for multi-chain support
-CREATE TABLE multisig_transactions_partitioned (
-  -- same columns
+-- LIST partition by chain_id (matches nonce-based query pattern)
+CREATE TABLE multisig_transactions (
+  chain_id INTEGER NOT NULL,
+  safe_address BYTEA NOT NULL,
+  safe_tx_hash BYTEA NOT NULL,
+  nonce INTEGER NOT NULL,
+  created TIMESTAMP NOT NULL,
+  -- ... other fields
 ) PARTITION BY LIST (chain_id);
 
-CREATE TABLE multisig_transactions_chain_1 
-  PARTITION OF multisig_transactions_partitioned FOR VALUES IN (1);
+-- High-volume chains get dedicated partitions
+CREATE TABLE multisig_transactions_worldchain
+  PARTITION OF multisig_transactions FOR VALUES IN (480);
 
-CREATE TABLE multisig_transactions_chain_137 
-  PARTITION OF multisig_transactions_partitioned FOR VALUES IN (137);
+CREATE TABLE multisig_transactions_ethereum
+  PARTITION OF multisig_transactions FOR VALUES IN (1);
+  
+CREATE TABLE multisig_transactions_polygon
+  PARTITION OF multisig_transactions FOR VALUES IN (137);
+
+-- Low-volume chains grouped
+CREATE TABLE multisig_transactions_others
+  PARTITION OF multisig_transactions DEFAULT;
+
+-- PRIMARY INDEX: nonce-based queries (most common)
+CREATE INDEX idx_tx_chain_safe_nonce
+  ON multisig_transactions (chain_id, safe_address, nonce DESC);
+
+-- SECONDARY INDEX: time-based queries (export endpoint, rare)
+CREATE INDEX idx_tx_chain_safe_created
+  ON multisig_transactions (chain_id, safe_address, created DESC);
 ```
 
 ### 3. Use CTEs for Complex Queries