fix: hide disabled plugin database types from connection form picker

[datlechin]

Summary

• Filter the database Type picker in the connection form to only show types whose plugin is enabled
• When editing an existing connection whose plugin is disabled, the current type is still shown so the picker binding stays valid
• Calls loadPendingPlugins() to handle lazy plugin loading

Follow-up to #236.

Test plan

• Disable a plugin (e.g., MySQL) in Settings > Plugins
• Open the connection form (New Connection)
• Verify MySQL/MariaDB are not in the Type picker
• Re-enable the plugin, verify they reappear
• Edit an existing MySQL connection while the plugin is disabled — verify the type still shows in the picker

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Reset new-form type when default plugin is disabled

This logic only preserves picker validity for edit mode; in new mode it returns enabled even when the bound type (default .mysql) is no longer present. If MySQL is disabled and the user opens a new connection, the picker options omit MySQL but saveConnection()/testConnection() still read type, so the form can operate on a hidden disabled type unless the user manually changes it. Please ensure new forms also reconcile type to an enabled value when the current selection is missing.

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