feat: Enable agent auto-discovery and add source location indicators

[robotdad]

Summary

This PR enables agent auto-discovery from .amplifier/agents/ and ~/.amplifier/agents/ directories, and enhances the /agents CLI command to show where each agent comes from.

Changes

1. Fix: Enable agent auto-discovery in foundation profile

Problem: The foundation profile was missing the agents: field, which prevented automatic discovery of agents from:

• .amplifier/agents/ (project level)
• ~/.amplifier/agents/ (user level)
• Collection agents

Solution: Added agents: all to the foundation profile YAML, which triggers the agent loading system to discover agents from all configured search paths.

File changed: amplifier_app_cli/data/collections/foundation/profiles/foundation.md

2. Enhancement: Add source location indicators to /agents command

Feature: The /agents command now displays the source location next to each agent name:

• (project) - from .amplifier/agents/
• (user) - from ~/.amplifier/agents/
• (bundle) - from bundle/collection

This helps users understand:

• Where agents come from
• Which agents are editable (project/user vs read-only bundle agents)
• Agent precedence (project > user > bundle)

File changed: amplifier_app_cli/main.py

Testing

Before

# Create agent in user directory
mkdir -p ~/.amplifier/agents
echo '---
name: my-agent
description: Test agent
---
You are a test agent.' > ~/.amplifier/agents/my-agent.md

amplifier  # Using foundation profile
> /agents
# Result: Agent not loaded

After

amplifier  # Using foundation profile  
> /agents

Available Agents (3 loaded)

explorer (bundle)
  Description: Deep local-context reconnaissance...

my-agent (user)
  Description: Test agent...

Impact

• Users can now drop agent files into .amplifier/agents/ or ~/.amplifier/agents/ and they'll be automatically available
• Source visibility makes it clear which agents can be edited
• No breaking changes - existing workflows continue to work

Related

This is Phase 1 of a larger enhancement plan inspired by Claude Code's agent management features. Future phases will add interactive creation, editing, and deletion capabilities.

See: https://code.claude.com/docs/en/sub-agents