__traceback_info__ containing a double quote corrupts the frame tooltip markup

Goal

Escape __traceback_info__ for use inside an HTML attribute, so that a value
containing a double quote cannot corrupt the traceback summary markup.

Done when: a __traceback_info__ value containing " renders as readable text
in the frame tooltip instead of terminating the attribute, and a test covers it.

Reproduction (reproduces on Python 3.9 through 3.14):

from backlash.tbtools import get_current_traceback
def f():
    __traceback_info__ = 'expected "quoted" value'
    raise ValueError('boom')
try:
    f()
except Exception:
    tb = get_current_traceback()
print([l for l in tb.render_summary().splitlines() if 'title' in l][0])

Current output - the attribute ends at the first inner quote, and the remaining
text is parsed as further attributes, so the tooltip shows only expected:

<li title="expected "quoted" value"><div class="frame" id="frame-...">

Cause: backlash/tbtools.py renders ' title="%s"' % escape(frame.info), and
backlash.utils.escape only translates " when called with quote=True, which
this call site does not do. Escaping &, < and > is sufficient for element
text but not for an attribute value.

Suggested minimal fix: pass quote=True at that call site. Alternatively,
backlash.utils.escape could be replaced by html.escape from the standard
library, whose quote parameter defaults to True; that is a wider change
because the helper has other call sites.

Why

__traceback_info__ is the Paste-era convention for attaching context to a
frame, and the values developers attach are frequently quoted strings: a SQL
statement, a template name, a repr of a parameter dict. Any double quote in
that value truncates the tooltip, so the frame annotation is unreliable
precisely for the values it exists to display.

This is the only place in the codebase where escaped output is written into an
HTML attribute; every other interpolation (filename, current_line,
exception, title) targets element text, where the current escape default
is correct. So the fix is a single call site, not a broader audit.

Verified as pre-existing rather than a regression: the same reproduction fails
identically on the commit preceding the recent modernization work.

References

• backlash/tbtools.py (Traceback.render_summary, the frame.info title
  attribute; Frame.info is populated from __traceback_info__)
• backlash/utils.py (escape, note the quote=False default)
• tests/test_tbtools.py may be a natural home for a regression test

Start in backlash/tbtools.py at Traceback.render_summary, where frame.info is used for the title attribute, and review backlash/utils.py to understand escape's quote handling. Add a regression test in tests/test_tbtools.py using a quoted traceback_info value. Done means the rendered tooltip preserves the quoted text and the test passes.