Enhance documentation for data model and import/export processes

- Updated data model documentation to clarify relationships between projects, scenarios, and profitability calculations.
- Introduced a new guide for data import/export templates, detailing CSV and Excel workflows for profitability, capex, and opex data.
- Created a comprehensive field inventory for data import/export, outlining input fields, derived outputs, and snapshot columns.
- Renamed "Initial Capex Planner" to "Capex Planner" and "Processing Opex Planner" to "Opex Planner" for consistency across user guides.
- Adjusted access paths and related resources in user guides to reflect the new naming conventions.
- Improved clarity and consistency in descriptions and instructions throughout the user documentation.

userguide/README.md

@@ -4,5 +4,5 @@ CalMiner user-facing documentation is organized by feature area. Start with the
 
 ## Available Guides
 
-- [Initial Capex Planner](initial_capex_planner.md) — capture upfront capital components, run calculations, and persist snapshots for projects and scenarios.
-- [Processing Opex Planner](processing_opex_planner.md) — manage recurring operational costs, apply escalation/discount assumptions, and store calculation snapshots.
+- [Capex Planner](initial_capex_planner.md) — capture upfront capital components, run calculations, and persist snapshots for projects and scenarios.
+- [Opex Planner](opex_planner.md) — manage recurring operational costs, apply escalation/discount assumptions, and store calculation snapshots.