do not set db_url to sqlite by default

[adhami3310]

since database modules are not installed by default, this provides a broken user experience as health metrics fail because db modules aren't isntalled

[greptile-apps]

Greptile Summary

This PR changes the default value of db_url in BaseConfig from "sqlite:///reflex.db" to None, preventing health check failures for users who don't have database modules installed. All downstream consumers (check_db_used, check_db_initialized, check_schema_up_to_date, Model.get_db_engine) already handle None gracefully, and tests that exercise SQLite explicitly mock the URL — so the impact is safely scoped.

Confidence Score: 5/5

Safe to merge — single-line default change with no functional regressions.

All code paths that read db_url already guard against None, tests mock the value explicitly, and the docker example sets the URL via an env var. No P0/P1 issues found.

No files require special attention.

Important Files Changed

Filename	Overview
packages/reflex-base/src/reflex_base/config.py	Changes the default db_url from "sqlite:///reflex.db" to None; all downstream consumers handle None cleanly.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[App startup] --> B{check_db_used}
    B -- "db_url is None - new default" --> C[Skip DB health check and schema checks]
    B -- "db_url is set explicitly" --> D[Run DB health check]
    D --> E{DB modules installed?}
    E -- Yes --> F[Health check passes]
    E -- No --> G[Health check fails]

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_{Reviews (1): Last reviewed commit: "do not set db_url to sqlite by default" | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 9 untouched benchmarks

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_{Comparing do-not-set-db_url-to-sqlite-by-default (3373b95) with main (cc7436c)}