feat: Add SQL event sourcing engine demonstrating database as events

sql_event_sourcing/README.md

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+# SQL Event Sourcing Engine
+
+This module demonstrates how a SQL database is fundamentally an event sourcing system.
+
+## Core Insight
+
+Every SQL operation is an event:
+- `INSERT` → `row_inserted(Table, RowId, Values)`
+- `UPDATE` → `row_updated(Table, RowId, OldValues, NewValues)`
+- `DELETE` → `row_deleted(Table, RowId, OldValues)`
+- `CREATE TABLE` → `table_created(Name, Schema)`
+
+The current state is always derived by replaying all events. Traditional databases optimize this with snapshots and indexes, but the fundamental model is event sourcing.
+
+## Usage
+
+```prolog
+?- use_module(sql_event_sourcing/sql_es).
+
+% Create a table (emits table_created event)
+?- create_table(users, [col(id, integer), col(name, varchar)]).
+
+% Insert rows (emits row_inserted events)
+?- sql_insert(users, [id-1, name-'Alice']).
+?- sql_insert(users, [id-2, name-'Bob']).
+
+% Query using CQL-style syntax
+?- users :: [id-Id, name-Name].
+Id = 1, Name = 'Alice' ;
+Id = 2, Name = 'Bob'.
+
+% Update (emits row_updated event with old/new values)
+?- sql_update(users, [name-'Robert'], [id-2]).
+
+% Delete (emits row_deleted event preserving old values)
+?- sql_delete(users, [id-1]).
+
+% View complete event log
+?- print_events.
+
+% View current state (derived from events)
+?- print_state.
+```
+
+## CQL-Style Term Format
+
+Following [SWI-Prolog's CQL](https://www.swi-prolog.org/pldoc/man?section=cql):
+
+| Operation | Syntax |
+|-----------|--------|
+| SELECT | `table :: [col-Var, ...]` |
+| SELECT with WHERE | `sql_select(table, [col-Var], [where_col-val])` |
+| INSERT | `sql_insert(table, [col-val, ...])` |
+| UPDATE | `sql_update(table, [col-newval], [where_col-val])` |
+| DELETE | `sql_delete(table, [pk_col-val])` |
+
+## Transaction Support
+
+```prolog
+?- begin_transaction.
+?- sql_insert(orders, [id-1, total-100]).
+?- sql_update(inventory, [qty-99], [id-5]).
+?- commit_transaction.   % or rollback_transaction
+```
+
+## Event Sourcing Benefits
+
+1. **Complete Audit Trail**: Every change is recorded with timestamps
+2. **Time Travel**: Reconstruct state at any point by replaying events up to that time
+3. **Debugging**: See exactly what happened and when
+4. **Undo/Redo**: Events contain enough info to reverse operations
+
+## Running the Demo
+
+```bash
+swipl -s sql_event_sourcing/sql_es_demo.pl -g run_demo
+```
+
+## Running Tests
+
+```bash
+swipl -s sql_event_sourcing/sql_es_demo.pl -g run_tests_sql -g halt
+```
+
+## Files
+
+- `sql_es.pl` - Core event sourcing SQL engine
+- `sql_es_demo.pl` - Demonstrations and unit tests