fix: align SQL execute gutter icon to actual statement start line

[Blankll]

Problem

The SQL execute gutter icon was displayed on the wrong line when statements are separated by blank lines or comment lines. For example:

-- Top-selling products by quantity     ← icon was here (L1, correct by luck)
SELECT
  ...
  total_sold DESC LIMIT 5;
                                        ← icon was HERE (L12, blank after ;)
-- Low stock inventory alerts
SELECT                                ← should be HERE (L15)
  ...

The scanner's bufStart sits right after the previous ;, so startLineNumber reflected the position of that blank/comment line instead of the first actual SQL content.

Fix

Added skipLeadingComments() function that scans leading lines and skips:

• Whitespace-only (blank) lines
• -- line comments
• /* */ block comments

The first line with actual SQL content determines the gutter icon position.

Before vs After

Statement	Before	After	Aligns with
1	L1 (comment header)	L2	SELECT
2	L12 (blank after ;)	L15	SELECT
3	L23 (blank after ;)	L25	SELECT
4	L37 (blank after ;)	L39	SELECT

Verification

• 446 existing tests pass (no regressions)
• 3 new test cases covering blank-line-separated, comment-separated, and adjacent statements
• Lint clean