[feat : feed notification] add notifications system in-app and email/Slack story scheduled delivery

[socallmebertille]

Summary

Notifications inbox & activity feed

• A single feed that merges your automations and notifications

• An unread indicator in the sidebar so you can see when you just received one notification

• Mark individual items as read, or mark everything as read at once; clicking a notification takes you straight to the relevant page

• A new filter/sort bar to narrow the feed down (by type, read status, users origin, etc.) and reorder it

Notifications kinds (in-app & by email)

• When owner set subscriptions

• Story refreshes when owner set the subscription

• Shared with you story or chat

• Feedback (+ or -) — for data-team admins

• Budget alerts — admins (and users when budget is fixed per-user) are notified when a provider budget limit is reached

Scheduled story delivery

• Stories can be set up to automatically re-run and be delivered on a schedule (or alongside their refresh)

• Choose who receives them — specific people or everyone with access

• Delivered via email/Slack, with the latest version of the story attached as a PDF

• Email as also (in addition to the attached PDF) the HTML in the email body

Per-story subscription controls

• A "Notifications for this story" dialog lets each person choose whether they want story updates by email and/or Slack, and change their mind anytime

One-click unsubscribe

• Every email and Slack notification includes a secure unsubscribe link

Behind the scenes

• A one-time backfill so recent past activity (shares, refreshes from the last ~90 days) shows up in the new feed right away

Related issues

Fix #659
Fix #660

[github-actions]

🚀 Preview Deployment

URL	https://pr-1424-dc0675b.preview.getnao.io
Commit	dc0675b

⚠️ No LLM API keys configured - you'll see the API key setup flow when trying to chat.

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