Add tags and filtering system for cards

[cuevaio]

Description

Add a tagging system for cards and the ability to filter the board view by tags, author, and other criteria.

Features

Tags

• Add tags to cards: Assign one or more tags to each card
• Tag management: Create, edit, and delete tags with custom colors
• Quick tagging: Easy UI to add/remove tags from cards

Filtering

• Filter by tag: Show only cards with specific tags
• Filter by author: Show only cards created by specific users
• Multiple filters: Combine filters (e.g., tag + author)
• Search: Text search within card content

UX Considerations (Important)

The filtering UI must clearly communicate that hidden cards still exist:

• Filter indicator: Prominent badge showing "Showing X of Y cards"
• Dimmed vs hidden: Consider dimming filtered-out cards instead of hiding completely (optional toggle)
• Clear filters button: Always visible when filters are active
• Empty state messaging: "No cards match your filters" with clear action to reset
• Filter panel: Sidebar or dropdown showing active filters
• Pulse/highlight: Subtle animation when filters are applied/removed

Acceptance Criteria

• Add/remove tags on cards
• Tag color customization
• Filter by tag (single and multiple)
• Filter by author
• Clear visual indicator when filters are active
• "Showing X of Y cards" counter always visible when filtered
• Easy way to clear all filters
• Filtered state syncs correctly (each user has their own filter view)
• Tags themselves sync in real-time across users