fix: remove reaction counts that read as thread-wide sentiment

[katomm]

• The thread header strip no longer carries a reaction count. Its other numbers cover the whole thread, so a count that only ever belonged to the opening post read as the sum of every thumb in the discussion.
• Reaction counts on a normal topic stay under the opening post itself, where it is clear which post they belong to.
• The opening post of a governance action can no longer be reacted to at all. It is a neutral mirror of an on-chain action, and a stake-free thumbs up next to the real tally read as a rival vote.
• Reactions on comments are unchanged, on governance actions and everywhere else.
• A reaction recorded on a governance opening post before this change is no longer shown and can still be withdrawn.