polish(ios): drop redundant centered title on connection tabs

[datlechin]

Summary

• Drops the centered navigation title on the four connection tabs (Tables, Query, History, Info). The bottom tab bar already labels the active tab, so the centered title was redundant.
• On Tables and Query the title was the connection name (TablePro); on History and Info it was just the tab name (History, Info). All four now show no centered title.
• Frees toolbar room for the database picker, schema picker, and edit button — noticeable on iPhone widths where the Info tab previously had 5 toolbar items competing for space.
• Outer .navigationTitle(connection.name) on ConnectedView.swift:35 kept intact for VoiceOver screen identification when entering from the connection list; doesn't show in the inner tab toolbar.
• tabTitle(_:) helper removed (was only called from the line being deleted).

Test plan

• Open a connection, switch through Tables / Query / History / Info — no centered title appears in any tab toolbar.
• Database picker and schema picker still render and function on tabs that have multiple databases / schemas.
• Info tab still shows the pencil edit button.
• Push into a table from Tables tab — the table name still shows as the title on the data browser screen.
• VoiceOver: enter a connection from the list, confirm the connection name is announced once on entry.