feat: make AI chat locale aware

[AdityaHegde]

We added language selection support. But AI chat responses were still in english.

Adding a locale param to router_agent. This is pulled from paraglide so the langauge matches the rest of the UI.

Only analyst_agent is locale aware, other parts will be updated before merging.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!