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.txt

@@ -0,0 +1,48 @@
+# ============================================
+# CXInsights - Requirements (Pinned Versions)
+# ============================================
+# Install: pip install -r requirements.txt
+# Install with PII: pip install -r requirements.txt -r requirements-pii.txt
+# ============================================
+
+# === Core Dependencies ===
+pydantic>=2.5.0,<3.0.0
+python-dotenv>=1.0.0,<2.0.0
+pyyaml>=6.0.1,<7.0.0
+orjson>=3.9.0,<4.0.0
+jsonschema>=4.20.0,<5.0.0
+
+# === STT (Speech-to-Text) ===
+assemblyai>=0.23.0,<1.0.0
+httpx>=0.25.0,<1.0.0
+
+# === LLM (Language Models) ===
+openai>=1.12.0,<2.0.0
+tiktoken>=0.5.0,<1.0.0
+tenacity>=8.2.0,<9.0.0
+
+# === Data Processing ===
+pandas>=2.1.0,<3.0.0
+duckdb>=0.9.0,<1.0.0
+numpy>=1.26.0,<2.0.0
+
+# === CLI ===
+typer>=0.9.0,<1.0.0
+rich>=13.7.0,<14.0.0
+
+# === Visualization (Dashboard) ===
+streamlit>=1.29.0,<2.0.0
+plotly>=5.18.0,<6.0.0
+matplotlib>=3.8.0,<4.0.0
+
+# === Exports ===
+openpyxl>=3.1.0,<4.0.0
+reportlab>=4.0.0,<5.0.0
+Pillow>=10.0.0,<11.0.0
+
+# === Async Support ===
+aiofiles>=23.2.0,<24.0.0
+asyncio-throttle>=1.0.0,<2.0.0
+
+# === Logging ===
+structlog>=24.1.0,<25.0.0