Agents page: filtering by tags, status, and name

[vybe]

Summary

Add filtering capabilities to the Agents page so users can quickly find agents by tags, running status, and name.

Filters

1. By name — text search/filter input that filters the agent list as you type
2. By status — filter by Running / Stopped / All
3. By tags — clickable tag chips or multi-select dropdown to filter by one or more tags

Acceptance Criteria

• Name filter: text input that filters agents list in real-time
• Status filter: toggle or dropdown for Running / Stopped / All
• Tag filter: select one or more tags to filter agents
• Filters are combinable (AND logic — name + status + tags)
• Filter state persisted in localStorage across page reloads
• Clear all filters button
• Agent count shown reflecting active filters (e.g., "Showing 5 of 12 agents")

Context

As the number of agents grows, users need filtering tools to quickly locate specific agents. The Dashboard already has tag-based filtering — this brings similar capability to the Agents page.

References

• Existing tag system: docs/memory/feature-flows/agent-tags.md
• Dashboard filter persistence (FILTER-001) for localStorage pattern

[vybe]

Implemented Agents page filtering with name search, status filter (All/Running/Stopped), multi-tag selection, combined AND logic, localStorage persistence, clear all filters button, and 'Showing X of Y' agent count. All changes in src/frontend/src/views/Agents.vue.