feat: Add Streamlit dashboard with Blueprint compliance (v2.1.0)

Dashboard Features:
- 8 navigation sections: Overview, Outcomes, Poor CX, FCR, Churn, Agent, Call Explorer, Export
- Beyond Brand Identity styling (colors #6D84E3, Outfit font)
- RCA Sankey diagram (Driver → Outcome → Churn Risk flow)
- Correlation heatmaps (driver co-occurrence, driver-outcome)
- Outcome Deep Dive (root causes, correlation, duration analysis)
- Export functionality (Excel, HTML, JSON)

Blueprint Compliance:
- FCR: 4 categories (Primera Llamada/Rellamada × Sin/Con Riesgo de Fuga)
- Churn: Binary view (Sin Riesgo de Fuga / En Riesgo de Fuga)
- Agent: Talento Para Replicar / Oportunidades de Mejora
- Fixed FCR rate calculation (only FIRST_CALL counts as success)

Technical:
- Streamlit + Plotly for interactive visualizations
- Light theme configuration (.streamlit/config.toml)
- Fixed Plotly colorbar titlefont deprecation

Documentation:
- Updated PROJECT_CONTEXT.md, TODO.md, CHANGELOG.md
- Added 4 new technical decisions (TD-014 to TD-017)
- Created TROUBLESHOOTING.md with 10 common issues

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

requirements-dev.txt

@@ -0,0 +1,26 @@
+# ============================================
+# CXInsights - Development Dependencies
+# ============================================
+# Install: pip install -r requirements-dev.txt
+# ============================================
+
+# === Testing ===
+pytest>=7.4.0,<8.0.0
+pytest-cov>=4.1.0,<5.0.0
+pytest-asyncio>=0.23.0,<1.0.0
+pytest-mock>=3.12.0,<4.0.0
+
+# === Type Checking ===
+mypy>=1.8.0,<2.0.0
+types-PyYAML>=6.0.0,<7.0.0
+pandas-stubs>=2.1.0,<3.0.0
+
+# === Linting & Formatting ===
+ruff>=0.1.0,<1.0.0
+
+# === Notebooks ===
+jupyter>=1.0.0,<2.0.0
+ipykernel>=6.27.0,<7.0.0
+
+# === Pre-commit Hooks ===
+pre-commit>=3.6.0,<4.0.0