[PREMIUM-001] Add premium plan and entitlements

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Outline

Summary

Adds the central premium entitlement system: named entitlement keys with free and premium values, a server-side isPremiumUser check backed by the subscription table and the env allowlist, server-enforced caps on profile saves and bumps, and a premium flag on discovery profile data so cards render premium cosmetics for real subscribers.

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Changes & Enhancements

• Type of Change:
  • Feature
  • Bugfix
  • Refactor
  • Chore
• Changes:
  • (Entitlements):
    • Rework src/lib/entitlements.ts around named keys: profile.targetLanguages, profile.tags, and discovery.bumpCooldownMs limits plus premium-only features (profile.voiceIntro, profile.cardThemes, privacy.hiddenVisits, notifications.profileViews).
    • Add src/lib/entitlements.server.ts with isPremiumUser, combining the env allowlist and active subscription state.
    • Source the scattered language, tag, and bump-cooldown constants from the entitlement table.
  • (Server):
    • Profile save enforces the language and tag caps at the caller's real entitlement level (premium users could previously never save past the free language cap).
    • Bump cooldown and discovery page use isPremiumUser so a paid subscription grants the shorter cooldown without env changes.
  • (Discovery):
    • Profile queries join subscriptions and set premium on discovery profiles, so premium card themes and badges reflect actual entitlement.
  • (Profile editor):
    • The profile route passes the viewer's entitlement, unlocking premium caps, card themes, and the voice intro editor for subscribers.

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Page / App Changes

Affected Next.js Routes (Local):

• /[lang]/profile (premium caps and unlocked premium controls for subscribers)
• /[lang] (discovery cards carry real premium status)

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 #89 and includes its commits until that merges; merge #89 first and this PR's diff reduces to the entitlement 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.