feat(skills): add deep-research skill

Copy deep-research skill from local Qoder installation to config repo for version control

skills/deep-research/templates/research_brief_template.md

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+# Research Brief Template
+
+## Purpose
+Standard output format for `quick` mode research. Concise, actionable, evidence-based.
+
+## Template
+
+```markdown
+# Research Brief
+
+**Title**: [Descriptive title in sentence case]
+**Date**: [YYYY-MM-DD]
+**Mode**: Quick Research Brief
+**AI Disclosure**: This brief was produced with AI-assisted research tools. All findings are verified against cited sources.
+
+---
+
+## Executive Summary
+[100-150 words. State the question, key findings, and main implication.]
+
+---
+
+## Background & Research Question
+
+### Context
+[2-3 paragraphs providing necessary background for the reader.]
+
+### Research Question
+> [The refined research question, as a single clear sentence.]
+
+### Scope
+- **In scope**: [what this brief covers]
+- **Out of scope**: [what this brief does not cover]
+
+---
+
+## Key Findings
+
+### Finding 1: [Title]
+[2-3 sentences with citation(s)]
+
+**Evidence strength**: [Strong / Moderate / Emerging]
+**Source(s)**: [Brief citation]
+
+### Finding 2: [Title]
+[2-3 sentences with citation(s)]
+
+**Evidence strength**: [Strong / Moderate / Emerging]
+**Source(s)**: [Brief citation]
+
+### Finding 3: [Title]
+[2-3 sentences with citation(s)]
+
+**Evidence strength**: [Strong / Moderate / Emerging]
+**Source(s)**: [Brief citation]
+
+[Add more findings as needed, typically 3-5]
+
+---
+
+## Analysis & Implications
+
+### What This Means
+[2-3 paragraphs interpreting the findings. Connect evidence to practical implications.]
+
+### Recommendations
+1. [Actionable recommendation with evidence basis]
+2. [Actionable recommendation with evidence basis]
+3. [Actionable recommendation with evidence basis]
+
+---
+
+## Limitations
+- [Limitation 1: e.g., search scope, time constraints]
+- [Limitation 2: e.g., evidence gaps]
+- [Limitation 3: e.g., AI-assisted analysis limitations]
+
+---
+
+## References
+[APA 7.0 format, 5-10 references typical for quick mode]
+
+1. [Reference 1]
+2. [Reference 2]
+...
+```
+
+## Usage Notes
+- Target length: 500-1,500 words
+- Minimum 5 cited sources
+- Every finding must have at least one citation
+- Evidence strength ratings should align with source quality hierarchy
+- Keep language accessible — this is a brief, not a journal article