[PREMIUM-003] Add premium discovery boosts

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Outline

Summary

Adds premium discovery boosts: premium members get three boosts per month that lift their profile to the top of the default discovery ordering for 24 hours, with usage tracked server-side, replay blocked while a boost is active, and status shown in the profile editor.

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Changes & Enhancements

• Type of Change:
  • Feature
  • Bugfix
  • Refactor
  • Chore
• Changes:
  • (Database):
    • Add boosted_until on profiles and a profile_boosts usage table.
    • Add the discovery.monthlyBoosts entitlement (free 0, premium 3) and boost status helpers in src/db/boosts.ts.
  • (Server):
    • Add POST /api/profile/boost: premium only, public profile required, 409 while a boost is active, 429 when the monthly allowance is spent, tracks a profile.boost analytics event.
  • (Discovery):
    • Discovery profiles carry a boosted flag only while the owner is still premium; the default recently-bumped sort places boosted profiles first, while explicit name, overlap, and match-score sorts stay relevance-driven. Blocking and visibility filters apply before boosts.
    • The feed tracks a discovery.boost_impressions analytics event with the boosted card count.
  • (Profile editor):
    • The options menu shows Boost profile with the remaining monthly count, a disabled Boost active state, and an error banner on failure.

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Page / App Changes

Affected Next.js Routes (Local):

• /[lang] (boosted profiles rank first in the default sort)
• /[lang]/profile (boost action and status in the options menu)

Before (Screenshot)

After (Screenshot)

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Component / Storybook Changes

Affected Storybook Components (Local):

Before (Screenshot)

After (Screenshot)

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Not Doing

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Other (Remarks)

Builds on #91 (and #90, #89) and includes their commits until they merge; merge those first and this diff reduces to the boost work.

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Checklists

• Code is well-documented (comments, JSDoc, etc.).
• Existing comments were updated as needed.
• No out-of-scope changes are included.
• Write TODO comments where future work is required.
• Removed unnecessary debug code (e.g., console.log, debugger).
• Self-reviewed and tested locally.