feat(postgres): initial stable release v0.9.0

pgx v5-native PostgreSQL client with launcher lifecycle, health check, unit-of-work via context injection, and structured error mapping.

What's included:
- Executor / Tx / Client / Component interfaces using pgx native types (pgconn.CommandTag, pgx.Rows, pgx.Row)
- New(logger, cfg) constructor; pgxpool initialised in OnInit
- Config struct with env-tag support for all pool tuning parameters
- UnitOfWork via context injection; GetExecutor(ctx) returns active Tx or pool
- HandleError mapping pgerrcode constants to xerrors codes (AlreadyExists, InvalidInput, NotFound, Internal)
- health.Checkable at LevelCritical; HealthCheck delegates to pgxpool.Ping

Tested-via: todo-api POC integration
Reviewed-against: docs/adr/

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 NOCHEBUENADEV
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.