fix: usability issues on the backend for managing invites

[abelanger5]

Description

Fixes several backend issues related to tenant invites:

1. Invite emails were not lowercased when created, which meant that casing which doesn't match the user email address (always lowercased) wouldn't register as a valid invite
2. Users were allowed to create duplicate invites for the same email address
3. Accepting a tenant invite when you were already a member would just be a silent no-op -- resolved by the above but fixed anyway.

Type of change

• Bug fix (non-breaking change which fixes an issue)

What's Changed

• Updated handlers to fix issues listed above.

Checklist

Changes have been:

• Tested (unit, integration, or manually with steps specified) -- manual
• Linted and formatted

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🤖 AI Disclosure

• I acknowledge that an LLM was used in the creation of this Pull Request, in accordance with Hatchet's AI_POLICY.md.

• Details: Claude for implementing fixes

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Project	Deployment	Actions	Updated (UTC)
hatchet-docs	Ready	Preview, Comment	Jul 16, 2026 6:29pm

[github-actions]

⚠️ Optional test failure: The load-deadlock job failed on this PR (optimistic-scheduling=false). This check is non-mandatory and does not block merging, but may be worth investigating. View logs