fix(debugger): keep editor line numbers 1:1 with source for breakpoints

[andreahlert]

Part of #685 (item 6).

The bug

normalizeScript reformats the script for display in the panel editor. It trimmed leading/trailing blank lines, which shifts every line up. But breakpoints and the paused-line highlight match against the tokenizer's original line numbers (token.line). So a script whose _ attribute starts with a newline (extremely common in HTML) displayed on click on Monaco line 1 while the tokenizer has it on line 2. A gutter click stored the Monaco line; the breakpoint check compared the source line; they never matched.

That's the "breakpoints sometimes work" report: it worked only when there was no leading blank line. Setting breakpoints from code worked because that path uses source lines directly.

The fix

Make the editor's line numbers stay 1:1 with the source so there is a single coordinate system everywhere (gutter clicks, the breakpoint check, and the paused-line highlight).

• normalizeScript now de-indents horizontally only and never adds or removes lines. Leading/trailing blank lines are kept as empty lines, so Monaco display line N == token.line N. This fixes the gutter mismatch and the paused-line highlight at the root, without scattering offset math across every call site.
• pauseAt now waits for editorReady before drawing the current-line decoration (mirroring showLivePause). selectElement mounts Monaco asynchronously, so the old synchronous highlight was applied to the not-yet-mounted editor and dropped, which is why the paused line frequently showed no highlight on the first break. It now reuses applyLineDecoration.

Verification

• Algebraic check of normalizeScript on leading-newline, double-leading-newline, and no-leading-newline scripts: display line now equals source line in every case (previously off by the number of leading blank lines), and line count is preserved. No regression on the no-leading-newline case.
• End-to-end in the panel against a _="\n on click ... breakpoint ..." script: execution pauses at the breakpoint, the Monaco model shows the command on the correct line, and the current line is highlighted (it was not highlighted at all before).

Scope

Source-only change to src/ext/debugger.js. dist/ is intentionally left out: the committed dist/ is already stale relative to committed src/ (e.g. the htmx-detection guard), so a rebuild here would pull in unrelated drift. Rebuild dist/ separately at release.