feat(core): add interactive community plugin picker

[Krr0ptioN]

Summary

Adds a new interactive picker (<Leader>pc) to easily browse, install, and uninstall AstroCommunity plugins.

Features

• Visual Interface: Split-pane layout with Categories and Plugins.
• Search: Real-time filtering of categories and plugins.
• Status Indicators: Green checkmarks for installed plugins, Red 'X' for removed ones.
• Auto-Config: Modifies lua/community.lua automatically.
• Navigation: Full Vim-style navigation (h/j/k/l, <Tab>).
• Configurable Path: Supports vim.g.astrocommunity_config_path to customize the target configuration file location (defaults to lua/plugins/community.lua).

Changes

• Added lua/astrocommunity/community-picker/init.lua: Core logic for the picker UI.
• Added plugin/community_picker.lua: Auto-registration of the <Leader>pc keybinding.
• Updated README.md: Usage documentation.

[github-actions]

Review Checklist

Does this PR follow the [Contribution Guidelines](development guidelines)? Following is a partial checklist:

Proper conventional commit scoping:

• If you are adding a new plugin, the scope would be the name of the category it is being added into. ex. feat(utility): added noice.nvim plugin

• If you are modifying a pre-existing plugin or pack, the scope would be the name of the plugin folder. ex. fix(noice-nvim): fix LSP handler error

• Pull request title has the appropriate conventional commit type and scope where the scope is the name of the pre-existing directory in the project as described above

• README is properly formatted and uses fenced in links with <url> unless they are inside a [title](url)

• Entry returns a single plugin spec with the new plugin as the only top level spec (not applicable for recipes or packs).

• Proper usage of opts table rather than setting things up with the config function.

• Proper usage of specs table for all specs that are not dependencies of a given plugin (not applicable for recipes or packs).

[Uzaaft]

@Krr0ptioN This shouldnt be added to this repo. It should be a seperate plugin living outside of this repo.

[Krr0ptioN]

I was planning to do the same actually, then there was no clue regarding what kind of contributions are welcomed.

[Uzaaft]

Also fyi I've been working on a community.nvim package myself.