feat: add cookie consent to docs site

[dangrondahl]

Description

Add cookie consent to docs.kosli.com so visitors are informed about analytics
and usage tracking (e.g. Mixpanel), in line with GDPR/ePrivacy requirements.

kosli.com already uses Termly for cookie consent
(UUID: c98bfcd6-2f30-4f3c-b53c-d6dbd9b8c40c), and the www repo already
includes Termly's consent-sync.html for cross-domain consent syncing.
The goal is to reuse this consent on docs.kosli.com so users who have already
accepted on kosli.com don't see a second banner.

Mintlify supports gating analytics on a localStorage value via:

"integrations": {
  "cookies": {
    "key": "<localStorage key>",
    "value": "<expected value>"
  }
}

Tasks

• Inspect what exact localStorage key and value Termly writes on
  analytics consent (Termly stores JSON — confirm the key/value
  Mintlify's cookies config should match against)
• Add Termly script to docs.kosli.com (either same property UUID or a
  new sub-property under the same Termly org)
• Configure Termly's cross-domain consent sync so users who consented
  on kosli.com don't see a second banner on docs.kosli.com
  (via the existing consent-sync.html mechanism)
• Wire up Mintlify's cookies config in docs.json once the key/value is confirmed
• Ensure Mixpanel tracking (feat: integrate Mintlify with Mixpanel analytics #65) only fires after consent is given
• Test: accept on kosli.com → verify no banner on docs.kosli.com
• Test: banner dismissal persists across sessions

References

• Mintlify privacy integrations: https://www.mintlify.com/docs/integrations/privacy/overview
• Termly script in www repo: layouts/partials/head.html
• Termly consent sync: static/consent-sync.html
• Related: feat: integrate Mintlify with Mixpanel analytics #65 (Mixpanel integration)

[dangrondahl]

The Termly banner can be added to the current kosli.mintlify.app domain today via Mintlify's custom scripts support in docs.json. However, cross-domain consent sync (so users who already accepted on kosli.com don't see a second banner) requires the docs to be served from docs.kosli.com. Termly's sync mechanism uses an iframe pointing to kosli.com/consent-sync.html, which works between related domains but not between kosli.com and kosli.mintlify.app as they are unrelated origins. The sync part can be completed as part of the go-live cutover to docs.kosli.com.

[dangrondahl]

Agreed with @AlexKantor87 to do this post launch (v1)