feat(sql): run the statement at the cursor, splitter with offsets (#1148)

[ZhuchkaTriplesix]

Refs #1148

Changes

• SqlStatementSplitter returns statement ranges (start, end, line). Semicolons inside string literals, quoted identifiers, comments and PostgreSQL dollar quotes do not end a statement.
• SqlStatementSplitter.at(spans, offset): a caret inside a statement picks it; a caret on a blank line or after the last ; takes the statement above.
• DestructiveSqlDetector.splitStatements is built on the same scanner, so the destructive check and the cursor lookup split the same way.
• Ctrl/Cmd+Enter, Ctrl/Cmd+R and numpad Enter run the selection, else the statement at the cursor.
• F5 and Ctrl/Cmd+Shift+Enter run the selection, else the whole script (as before, sent as one string).
• Tests: splitting on quotes, comments, dollar quoting and empty statements; offsets and lines; caret inside, on a blank line, after the last ;, before the first statement, and in an empty script.

Not in this PR

• Script run one statement at a time with stop at the first error and the status Statement k of n failed (line L) — the driver still receives the whole script as one string.
• The Run ▾ split button, the destructive check per run over the statements that will actually run, and one history entry per run.
• Ctrl/Cmd+H (query history) and removal of F11 from the reference.

🤖 Generated with Claude Code

[github-actions]

Grid scroll benchmark

metric	base	PR	change
p50	11.01 ms	13.60 ms	+23.5% ⚠️
p90	21.14 ms	23.81 ms	+12.6% ⚠️
p99	47.36 ms	54.27 ms	+14.6% ⚠️
stutters	296.00	292.00	-1.4%

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