chore: commit pending phase-3 work and add TEST_ACCOUNTS.md

Includes planning artifacts (03-CONTEXT, 03-DISCUSSION-LOG, 03-02-SUMMARY),
integration test script, MinIO/auth/docker fixes, and local dev account reference.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/postgres/initdb.d/01-init-users.sql

@@ -6,7 +6,10 @@
 -- Migration user: DDL privileges (CREATE TABLE, ALTER TABLE, CREATE INDEX)
 CREATE USER docuvault_migrate WITH PASSWORD 'changeme_migrate';
 GRANT ALL PRIVILEGES ON DATABASE docuvault TO docuvault_migrate;
+-- PostgreSQL 15+: schema CREATE is not granted by default even with GRANT ALL ON DATABASE
+GRANT ALL ON SCHEMA public TO docuvault_migrate;
 
 -- App user: runtime DML only (SELECT, INSERT, UPDATE, DELETE) — no DDL
 CREATE USER docuvault_app WITH PASSWORD 'changeme_app';
 GRANT CONNECT ON DATABASE docuvault TO docuvault_app;
+GRANT USAGE ON SCHEMA public TO docuvault_app;