docs: refresh core database integration screenshots - #476

What this changes

This draft refreshes the current Deepnote UI screenshots for the predefined core-database-integrations batch:

• PostgreSQL setup and successful query state
• MySQL setup
• MongoDB setup
• Supabase PostgreSQL setup and successful query state

The SQL Server and InfluxDB pages were also audited through live workflows, but no existing static asset was replaced for those pages because their current evidence does not correspond to the documented static screenshot action.

How this was verified

• Used the real Google Chrome UI and only the approved Sample Workspace.
• Restored temporary TCP tunnels to disposable local PostgreSQL, MySQL, MongoDB, SQL Server, and InfluxDB v2 fixtures.
• Verified connection forms, schema browsing, SQL blocks, Python client execution, filtered query results, and DataFrame output where documented.
• Captured replacement screenshots from the exact Chrome window, removed browser chrome and cursors, verified native dimensions, and encoded each replacement directly to WebP under the repository byte limit.
• Ran validate_pr_diff.py against origin/main.
• Ran pnpm test: 2,894 tests passed and 1 test was skipped.
• Ran pnpm typecheck, pnpm prettier:check, and pnpm biome:check. Biome reported six pre-existing warnings in example files and a broken symlink; no fixes were applied.

Unverified by human

This draft uses the user-authorized incomplete-verification exception. The following exact gaps remain:

• Supabase: Supabase account and project creation; provider-issued database host, database, port, user, password; current Supabase provider screenshot R1viC2QvqEjetTO9FLzw.webp. The Deepnote PostgreSQL workflow was verified with disposable local data, but no Supabase account was available and the audit does not handle real credentials.
• InfluxDB: External Deepnote Templates workspace template duplication step; current external InfluxDB provider token-creation UI and screenshot; evidence did not verify the linked template workspace because the audit contract permits only Sample Workspace. The documented Python client and query path were verified with a disposable local InfluxDB v2 fixture.
• PostgreSQL, MySQL, and SQL Server: separate SSL and SSH connection behavior was not independently exercised because the disposable fixtures intentionally used plain TCP and did not provide SSH servers. The current setup controls were observed in the live forms.
• MongoDB: a separate secure transport or SSH connection was not independently exercised; the documented connection-string and Python query path were verified with disposable data.

No real provider account, password, API token, or private credential was handled. The replacement images use safe disposable test data or current Deepnote UI state only.