Add MariaDB and PostgreSQL database provider support

[bauerpawel]

Description

Adds MariaDB/MySQL and PostgreSQL as database backends, alongside the existing SQLite and Redis providers. Both implement dbabstraction.Database via pure-Go, CGO-free drivers (go-sql-driver/mysql, jackc/pgx/v5), track their own schema version, and create their tables on first connect — no separate migration tooling needed.

• New providers: internal/configuration/database/provider/mariadb, internal/configuration/database/provider/postgres
• Setup wizard: new form fields, JS toggling, and URL parsing for the mariadb:// and postgres:// schemes, plus a database name field on DbConnection
• database.Migrate() (used by --migrate-db) already worked generically via the Database interface, but the CLI's status-line getType() helper didn't know about the two new types and printed "Invalid" — fixed, and the existing test's expectation was updated accordingly
• make test-mariadb / make test-postgres targets to run each provider's test suite against a real, disposable database (no in-process mock exists for either engine, so these are gated behind mariadbtest/postgrestest build tags and excluded from CI, matching the existing awstest convention)
• Documents the mariadb:// and postgres:// URL schemes in advanced.rst, which previously only mentioned sqlite:// and redis://
• .gitignore entry for a local test-credentials file used for live testing against real servers (never committed)

Verified live against real MariaDB 11.8 and PostgreSQL 17 servers, including a full migration round trip (SQLite → MariaDB → PostgreSQL → SQLite) that preserved users, E2E info, API keys, file metadata, hotlinks, and file requests at every hop.

Type of Change

• New feature (non-breaking change which adds functionality)

Technical Details

• Database changes: Yes — adds two new Database provider implementations (MariaDB/MySQL, PostgreSQL); no changes to existing providers or their schemas.
• Storage backend affected: No
• Usage of AI: Yes — developed with Claude Code as a pair-programming assistant (provider implementations, setup wizard wiring, tests, docs). I reviewed and tested all changes, including live verification against real MariaDB/PostgreSQL servers, before submitting.

How Has This Been Tested?

• Manual Testing: Ran the setup wizard against real MariaDB 11.8 and PostgreSQL 17 servers; verified --migrate-db round-trips data correctly between all four supported database types.
• Unit Tests: go test ./... --tags=test,awsmock (full suite passes; mariadbtest/postgrestest-tagged tests run separately via make test-mariadb/make test-postgres against real servers)
• Environment: Windows 11

Checklist

• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

🤖 Generated with Claude Code

https://claude.ai/code/session_0168YUwGEzEHTqd9CwzXE53d