docs: update agents documentation for dashboard v2 UI and sync changes

[numnx]

This PR updates the agents documentation across docs and docs-web to reflect the current dashboard behavior and UI implementation. Specifically:

• docs/architecture/agent-preset-foundation.md: Aligned references to AgentMemoryConfigPanel, AgentMcpManageModal, AgentKnowledgePanel, and InstructionFileEditorPanel.
• docs/architecture/agent-sync-and-planning-agent.md: Updated out_of_sync status logic based on AgentPresetSyncService to correctly mention memory, avatar, and MCP checks.
• docs-web/user/dashboard/agents.md: Updated user guide for "Creating an agent" with details on Instruction Files, Knowledge Base, MCP access, and updated Memory and Avatar customization.

Note: No stale .jules-subagents references existed in docs/dashboard/design-system-agents.md or docs/architecture/agent-routing.md to be replaced.

---

PR created automatically by Jules for task 6276233535332921389 started by @numnx

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.