Fix #173: Exclusive bounties should not bypass tech stack filters

[arthurus36-alt]

This fixes #173 where the counts for technologies on the /bounties page (e.g. "Svelte (1)") did not match the actual number of displayed bounties when clicked.

The issue was caused by b.visibility == :exclusive or inside the :tech_stack criteria applicator in lib/algora/bounties/bounties.ex. Because of this condition, whenever a user filtered by a specific tech stack (e.g., Svelte), ALL :exclusive bounties on the platform were unconditionally included in the list, completely ignoring the user`s chosen tech filter.

By removing the b.visibility == :exclusive bypass from :tech_stack, users will now see precisely the bounties that match the technology they clicked.

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