Add admin user management

docs/db-schema-spec.md

@@ -5,17 +5,19 @@
 This document defines the database schema in an AI-agent-friendly format.
 
 - Source of truth: Alembic revisions in `migrations/versions`
-- Current baseline revision: `20260403_0003`
+- Current baseline revision: `20260403_0004`
 - Baseline files:
 	- `migrations/versions/20260403_0001_initial_portfolio_schema.py`
 	- `migrations/versions/20260403_0002_strategy_set_columns.py`
 	- `migrations/versions/20260403_0003_portfolio_strategy_refs.py`
+	- `migrations/versions/20260403_0004_users_table.py`
 
 ## 2. Scope
 
 Schema objects covered by baseline revision:
 
 - `strategy_sets`
+- `users`
 - `portfolios`
 - `portfolio_ledger`
 - secondary indexes
@@ -30,7 +32,29 @@ Schema objects covered by baseline revision:
 
 ## 4. Tables
 
-### 4.1 strategy_sets
+### 4.1 users
+
+Purpose:
+
+- Stores admin-managed user records for operational ownership and future identity mapping.
+
+Columns:
+
+| Column | Type | Null | Default | Constraints / Notes |
+|---|---|---|---|---|
+| id | Text | NO | - | Primary Key |
+| username | Text | NO | - | Unique username |
+| email | Text | YES | - | Unique when present |
+| created_at | DateTime(timezone=True) | NO | NOW() | Creation timestamp |
+| updated_at | DateTime(timezone=True) | NO | NOW() | Last update timestamp |
+
+Constraints:
+
+- Primary key: `id`
+- Unique: `uq_users_username` on (`username`)
+- Unique: `uq_users_email` on (`email`)
+
+### 4.2 strategy_sets
 
 Purpose:
 
@@ -52,7 +76,7 @@ Constraints:
 - Unique: `uq_strategy_sets_name_config` on (`name`, `config`)
 - Unique: `uq_strategy_sets_nick` on (`nick`)
 
-### 4.2 portfolios
+### 4.3 portfolios
 
 Purpose:
 
@@ -60,7 +84,7 @@ Purpose:
 
 Current baseline note:
 
-- The columns below describe the currently migrated schema through revision `20260403_0003`.
+- The columns below describe the currently migrated schema through revision `20260403_0004`.
 
 Columns:
 
@@ -90,7 +114,7 @@ Constraint notes:
 - `active_strategy_id` is a nullable logical reference to `strategy_sets.id`
 - `avabile_strategies` stores zero or more selectable strategy set IDs when present
 
-### 4.3 portfolio_ledger
+### 4.4 portfolio_ledger
 
 Purpose:
 
@@ -121,14 +145,21 @@ Constraints:
 
 ## 5. Indexes
 
-### 5.1 idx_portfolio_ledger_portfolio_time
+### 5.1 ix_users_created_at
+
+- Table: `users`
+- Columns/expressions: (`created_at`)
+- Unique: no
+- Intent: speed operational listing by recency.
+
+### 5.2 idx_portfolio_ledger_portfolio_time
 
 - Table: `portfolio_ledger`
 - Columns/expressions: (`portfolio_id`, `recorded_at DESC`)
 - Unique: no
 - Intent: fetch recent ledger entries per portfolio efficiently.
 
-### 5.2 idx_portfolios_broker_status_updated
+### 5.3 idx_portfolios_broker_status_updated
 
 - Table: `portfolios`
 - Columns/expressions: (`broker`, `status`, `updated_at DESC`)
@@ -170,3 +201,4 @@ When schema changes:
 | 20260403_0001 | migrations/versions/20260403_0001_initial_portfolio_schema.py | Initial schema for strategy sets, portfolios, ledger, indexes, optional hypertable |
 | 20260403_0002 | migrations/versions/20260403_0002_strategy_set_columns.py | Rename `strategy_name`->`name`, `strategy_config`->`config`, add unique `nick`, handle legacy unnamed unique constraint |
 | 20260403_0003 | migrations/versions/20260403_0003_portfolio_strategy_refs.py | Remove embedded portfolio strategy fields, add `active_strategy_id` and `avabile_strategies` |
+| 20260403_0004 | migrations/versions/20260403_0004_users_table.py | Add `users` table with unique username/email and created_at index |