feat: expand Copilot agents coverage

[2-Coatl]

Summary

• add an ExecPlan describing how to sync documented agents with the Copilot configuration
• register every agent definition under .agent/agents/ inside .github/copilot/agents.json with concise descriptions

Testing

• cat .github/copilot/agents.json | python3 -m json.tool
• for agent in $(jq -r '.agents[].instructions' .github/copilot/agents.json); do if [ -f "$agent" ]; then echo "[OK] $agent" else echo "[MISSING] $agent" fi done

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Codex Task

[Copilot]

Pull Request Overview

This PR expands GitHub Copilot's agent coverage by registering all documented agent definitions from .agent/agents/ into .github/copilot/agents.json. The update enables users to invoke specialized agents directly through Copilot without manually referencing their instruction files.

Key Changes:

• Added 37 new agent definitions across domain, provider, automation, SDLC, meta, quality, documentation, and TDD categories
• Created an ExecPlan documenting the synchronization strategy and validation steps
• All agent entries include concise Spanish descriptions and references to their markdown instruction files

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.github/copilot/agents.json	Added 37 agent definitions organized by functional categories (domain, providers, automation, SDLC, meta, quality, documentation, TDD)
.agent/execplans/EXECPLAN_expand_copilot_agents.md	New ExecPlan documenting the agent expansion process, validation steps, and completion criteria