Add management UI for repost cleanup

[matthewladams]

Motivation

• Provide a simple web-based management UI so saved posts/reposts can be reviewed and deleted during testing.
• Keep the UI lightweight and easy to style by using Tailwind via CDN.
• Make the UI optional and non-blocking so it can run alongside the Discord bot when configured.

Description

• Add a new management_ui.py Flask app that lists recent posts and exposes a POST /delete/<id> endpoint with Tailwind UI present in the template.
• Extend dbInteraction.py with is_db_available(), fetchPosts(limit), and deletePost(post_id) and guard DB calls when a connection is not present.
• Start the management UI from main.py in a daemon thread via a new start_management_ui() function and control it with TIKBOT_MANAGEMENT_UI_ENABLED and TIKBOT_MANAGEMENT_UI_PORT.
• Add flask to requirements.txt so the UI dependency is declared.

Testing

• Attempted to run the UI with python management_ui.py, which failed with ModuleNotFoundError: No module named 'flask' because the dependency was not available in the environment.
• Attempted to install the dependency with pip install flask, which failed due to network/proxy restrictions in the sandbox (package fetch blocked).
• No automated test suite (pytest) was run as part of this rollout due to the environment dependency issue.

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Codex Task