fix(discussions): simplify search syntax and avoid over filtering for edge cases

[setchy]

Combo PR

🧼 further simplification of discussions code

• rename and move search syntax function into graphql/utils.ts
• fetch only the most recent discussion
• move helper logic into api/client where it better belongs

🔧 fix a handful of edge-cases that occur when an old discussion is moved from done -> inbox as unread:

• remove updated:>timestamp+padding from search condition (notification timestamp doesn't match the discussion updatedAt under these conditions
• remove results filtering by viewerSubscription (discussion left as IGNORED when under these conditions)