#274: align editor line numbers with wrapped text rows

With wrap on, a logical line occupies several visual rows in the textarea
but the gutter showed one number per logical line, so every number after
the first wrapped line drifted off its text (the paste view fixed this in
#167; the editor gutter did not). Measure the wrapped row count per logical
line with a hidden mirror div sharing the editor's font and wrapping rules,
and render one .gutline block per visual row with the number on the first
row of its logical line. Re-measure on input, wrap toggle and resize.
Verified: gutter scrollHeight == textarea scrollHeight with zero diff at
1400x900 and 375x812, wrap on and off.

internal/web/static/app.css

@@ -319,8 +319,10 @@ html[data-wrap] .float { overflow-x: hidden; }
 .codebody { padding: 0 18px; white-space: pre; overflow-x: auto; }
 /* #167: each logical line is its own block so offsetTop identifies its first visual row */
 .codeline { display: block; }
-/* #167 rev: gutter number spans must stack one per visual row (wrap on) */
-.code .gutter .gutline { display: block; }
+/* #167: gutter number spans must stack one per visual row (wrap on).
+   #274: the /new editor gutter uses the same .gutline blocks when its own
+   wrap toggle is on, so scope the rule to any gutter, not just .code. */
+.code .gutter .gutline, .editor-wrap .gutter .gutline { display: block; }
 /* #194: codeline blocks are adjacent (no '\n' text between them), so an
    empty block (blank source line) needs its own line box to stay one row */
 .codeline:empty::before { content: "\200B"; }