fix(browser): report the caller's line and column for browser-run compile errors

[ankitranjan7]

Closes #353.

A program that fails to compile inside browser run was reported as
QuickJS promise rejected: invalid number literal with no position. The prefix
pointed at async plumbing rather than at the program, so readers audited
heredocs and await instead of the actual defect — an unescaped quote in a
string literal holding a URL.

Before / after

Real case from the task eval, a 2,361-character line:

✖  BROWSER_RUN_SYNTAX_ERROR: QuickJS promise rejected: invalid number literal
✖  Fix the browser-run JavaScript syntax and retry.

✖  BROWSER_RUN_SYNTAX_ERROR: invalid number literal at line 1, column 1215
  tput%3E%3Cscript%3Econst%20form%3Ddocument.querySelector('%23registration')%2Cdr
                                                             ^
✖  Your program failed to compile; the browser was never touched. A common cause
   is an unescaped quote when embedding a URL or HTML in a string literal — use
   double quotes or a template literal for values that contain apostrophes.

What changed

• Compile the program before racing it, so a compile failure is no longer a
  rejected promise wearing a host stage prefix.
• Report the caller's own line and column. new AsyncFunction(body) prepends two
  lines of wrapper, so those are subtracted — verified against QuickJS, which does
  supply lineNumber / columnNumber; they were simply being discarded.
• Emit a windowed excerpt with a caret so a 2,000-character line stays readable.
• Name the quoting cause in the hint.
• quickjs-host.ts#toError no longer prefixes errors that already carry a
  BROWSER_RUN_ code.

Drive-by

runner.test.ts imported MemorySnapshotBaselineStore twice, so the file failed
to load and its 74 tests had never run. The duplicate is removed here; all 74
pass.

Verification

• Reproduced the original failure against a local build, then confirmed the new
  output for both the minimal case and the real 2,361-character program.
• New regression test pins the line, column, source excerpt, absent prefix, and
  hint — this also pins the AsyncFunction two-line offset against future
  quickjs-ng upgrades.
• Unit suite: 2534 pass, 1 failure that is also present on main and unrelated
  (profile display, personal: connected v1.2.3). Baseline on main is 2460
  passing, so this adds 74 previously-dead tests.

🤖 Generated with Claude Code

[github-actions]

🟠 Maintainer review suggested — low confidence

The automated review could not reach a fully supported conclusion.

Limitations

• The automated review returned an invalid structured result.

This review is advisory and does not block merging.