UI: Consolidate parameter-related settings into Parameter Selection tab

[Gero1999]

Issue

Closes #1238

Description

Moves all parameter-related configuration into the Parameter Selection tab so users don't need to switch tabs to configure what gets calculated:

• Partial Interval Calculations → collapsible accordion below the parameter matrix
• Ratio Calculations → collapsible accordion below intervals
• Units button → header row, next to the PK parameter details button
• Detected Study Types → remains at the bottom (collapsible, unchanged)

The Settings tab is renamed to General Settings and now only contains: General Settings, Data Imputation, Flag Rule Sets, and the Download settings button.

All accordion sections in Parameter Selection are collapsed by default to keep the page clean.

How to test

1. Layout: Open the app → NCA Setup → verify "General Settings" and "Parameter Selection" tabs exist
2. Parameter Selection tab: Verify the matrix is at the top, followed by collapsed accordions for Partial Interval Calculations, Ratio Calculations, and Detected Study Types. Units and PK parameter details buttons should be in the header row.
3. Partial Intervals: Expand the accordion → Add Row → fill in an interval → Run NCA → verify the interval appears in results
4. Ratio Calculations: Expand the accordion → configure a ratio → Run NCA → verify ratio appears in results
5. Units button: Click it → verify the units modal opens and works as before
6. General Settings tab: Verify it contains General Settings, Data Imputation, Flag Rule Sets, and Download settings button — no Partial Intervals or Ratios
7. Settings round-trip: Download settings → reload → upload → verify all settings (including intervals and ratios) are restored

Contributor checklist

• Code passes lintr checks
• Code passes all unit tests
• New logic covered by unit tests
• New logic is documented
• App or package changes are reflected in NEWS
• Package version is incremented
• R script works with the new implementation (if applicable)
• Settings upload works with the new implementation (if applicable)

Notes to reviewer

No server logic was changed. All changes are UI reorganization:

File	What changed
settings.R	Extracted partial_intervals_ui() as standalone function. Removed the accordion panel from settings_ui(). Fixed stale accordion open parameter.
parameter_selection.R	Added units_ui, intervals_ui, ratios_ui parameters. Renders them in the header row and as accordion panels. Updated help dropdown.
nca_setup.R	Renamed tab to "General Settings". Passes UI elements to parameter_selection_ui() via args. Removed ratios/units from Settings tab.

Server wiring is preserved because all UI elements keep their original namespace IDs (e.g., partial_intervals_ui(ns(\"nca_settings\")) matches settings_server(\"nca_settings\", ...))."

[js3110]

Great idea! makes much more sense, and looks good and works well :D