feat(sql-workspace): one-row toolbar, Diagram on the tab strip (#1150)

[ZhuchkaTriplesix]

Refs #1150

Changes

• The toolbar is one row: Run (with its menu), Explain, Cancel while running, then the editor tools as icon buttons (History, Format, Open, Save) with tooltips, then the database name, the transaction badge, Commit / Rollback while a transaction is open, and Session ▾. On a narrow window the row scrolls sideways instead of wrapping.
• Begin is in Session ▾ only (its inline button is gone). The e2e transaction test opens the menu first.
• No Query caption and no Data Output bar; the results get the full height.
• Diagram moves to the right end of the query tab strip (SqlQueryTabBar.trailing), keeping the key open_diagram_tab.
• Tests: the toolbar stays on one row at 800 px; no caption and no bar.

Already on dev before this PR

• The transaction badge, and the Session menu with Autocommit, timeout, Begin and Preferences (ui(sql-workspace): transaction badge, Commit and Rollback only while a transaction is open (#1150) #1192, ui(sql-workspace): Session menu for autocommit, statement timeout, Begin and Preferences (#1150) #1193).

Not in this PR

• Labels hiding below a breakpoint (the row scrolls instead).
• The elapsed-time badge in the results toolbar (SqlExecutionResult.elapsed).
• Hiding Diagram when the connection has no diagram source (the extension workspace already sets showDiagram: false; other drivers are not checked here).
• Commit and Rollback inline only while a transaction is open are in place; the Diagram hide rule for connections without a source is not.

[github-actions]

Grid scroll benchmark

metric	base	PR	change
p50	15.52 ms	17.05 ms	+9.9% ⚠️
p90	24.68 ms	24.63 ms	-0.2%
p99	48.90 ms	55.36 ms	+13.2% ⚠️
stutters	299.00	288.00	-3.7%

Informational only (threshold 5%). Shared CI runners are noisy; re-run before trusting a single result.