Enable AI Chat history feature

[petemill]

• Resolves Enable AI Chat History feature by default brave-browser#42854

Adds requests from security and privacy review in order to accept the feature being enabled by default:

• Resolves AI Chat storage notice should dismiss only after the first prompt is sent brave-browser#42853

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[fallaciousreasoning]

🎉

[diracdeltas]

This should probably be done before this is merged? https://github.com/brave/reviews/issues/1703#issuecomment-2539690183 (please check with Pat if unclear)

[petemill]

The link in the notice now goes directly to the newly published sub-page about Storage https://support.brave.com/hc/en-us/articles/32663367857549-How-do-I-use-Chat-History-in-Brave-Leo

[diracdeltas]

maybe not specific to this PR, but this seems buggy:

1. enable AI history feature in nightly (1.75.95 for me)
2. open leo, disable page context
3. it shows me some suggestions but the icon next to them is blank? UPDATE: seems this is an apple problem

4. click on one of them, like 'formulate a business proposal'. notice the output.
5. close leo and reopen
6. click 'conversation history' > 'formulate a business proposal'
7. notice the conversation is blank

[petemill]

maybe not specific to this PR, but this seems buggy:

1. enable AI history feature in nightly (1.75.95 for me)
2. open leo, disable page context
3. it shows me some suggestions but the icon next to them is blank? UPDATE: seems this is an apple problem

4. click on one of them, like 'formulate a business proposal'. notice the output. 5. close leo and reopen 6. click 'conversation history' > 'formulate a business proposal' 7. notice the conversation is blank

@diracdeltas mentioned that emojis aren't working on any website for her, so I think we can ignore that part.

As for the second issue - the cause is:

• AI Chat is failing to persist an entry if it completes whilst the conversation has no UI attached brave-browser#42871

[diracdeltas]

no security comments from me, will let the privacy reviewer(s) approve.

[ShivanKaul]

I'm okay merging into Nightly as long as the privacy policy update is applied. Also, not blocking for Nightly, but these issues must be fixed before the feature is enabled beyond.

[petemill]

waiting for

• https://github.com/brave/brave-com/pull/2667

[brave-builds]

Released in v1.75.101