chore: add Bing verification token for the docs.truecalc.app site

[hhimanshu]

Summary

Adds the Bing Webmaster Tools verification token for the https://docs.truecalc.app/ site
entry, so BingSiteAuth.xml verifies it.

Why a second token

Bing scopes a site by URL prefix, not by domain the way a Google Search Console domain
property does. https://truecalc.app/ and https://docs.truecalc.app/ are two separate sites
in Bing and each needs its own token — unlike GSC, where the truecalc.app domain property
already covers every subdomain.

The existing token was issued for a different site entry, so Bing could not verify
docs.truecalc.app with it.

Why append rather than replace

<users> accepts multiple <user> children. Appending keeps the previously verified property
verified; replacing would have broken it.

<?xml version="1.0"?>
<users>
	<user>4A2DF37AEACD708CD051F4D161C07367</user>
	<user>8C5913DDDB5710E055911488CB4A9E96</user>
</users>

How to test

After deploy:

curl -s https://docs.truecalc.app/BingSiteAuth.xml
# expect both <user> tokens

python3 -c "import xml.etree.ElementTree as ET; \
  print([u.text for u in ET.parse('public/BingSiteAuth.xml').getroot().findall('user')])"
# => ['4A2DF37AEACD708CD051F4D161C07367', '8C5913DDDB5710E055911488CB4A9E96']

Then in Bing Webmaster Tools, add https://docs.truecalc.app/ and click Verify — it reads this
file at the site root. XML was validated well-formed locally.

Follow-ups (not in this PR)

• Submit https://docs.truecalc.app/sitemap.xml under the new Bing site
• Set the INDEXNOW_KEY secret to the key already live at
  /3e251d07d17245c16ae611b1990a681a.txt, then do a one-time --all seeding run (the default
  delta mode currently finds 0 changed URLs)
• The https://truecalc.app/ Bing entry points at a host with no DNS records and can only ever
  report errors — worth removing unless a site is planned for the apex

🤖 Generated with Claude Code

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