Channel names allow case-variant duplicates (e.g., general and General) causing routing conflicts

Description

Room name validation currently performs a case-sensitive duplicate check in getValidRoomName.
However, routing, mentions, and search treat room names case-insensitively.

Because of this mismatch, channels that differ only by letter casing can be created.

Example:

general
General

Both rooms coexist in the database, but the application resolves them to the same route.

Opening:

/channel/General

redirects to:

/channel/general

This leads to incorrect navigation and mention behavior.

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Steps to Reproduce

1. Create a channel named general
2. Create another channel named General
3. Both channels are created successfully
4. Visit /channel/General

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Expected behavior

The second channel creation should be rejected because channel names should be unique regardless of letter casing.

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Actual behavior

Both channels are created, but routing redirects to the lowercase version, causing inconsistent behavior with navigation, mentions, and search.

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Impact

• Incorrect channel routing
• Confusing mentions
• Broken navigation for users
• Duplicate logical channels

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Proposed Solution

Normalize the room name (e.g., lowercase) before duplicate validation to enforce case-insensitive uniqueness.

Start by locating getValidRoomName and inspect how it checks for duplicate channel names. Add coverage for creating both general and General, then verify that the second creation is rejected and that existing case-insensitive routing remains consistent.