Fix Next button stuck disabled after incomplete mapping error

[Gero1999]

Issue

Closes #1402

Description

In the Data tab, submitting an incomplete column mapping (a required variable unmapped) correctly showed an error notification, but the Next button then stayed permanently disabled — the user could not correct the mapping and continue, and had to restart the app.

Root cause

In inst/shiny/modules/tab_data.R (.setup_step_navigation):

• On click, the button is disabled unconditionally, and on the mapping step it only bumps trigger_mapping_submit (it does not change the step).
• The re-enable observer depended only on data_step():

  observe({
    data_step()
    shinyjs::enable("next_step")
  })

• On an incomplete mapping, apply_mapping() throws, mapped_data() catches it and returns NULL, so adnca_mapped() is NULL, req(adnca_mapped()) halts, and the step never advances. Since data_step() never changes, the re-enable observer never re-fires and the button stays disabled.

Fix

Make the re-enable observer also depend on trigger_mapping_submit(), which increments on every mapping submission. The Next button is now re-enabled after each submission is processed, whether the mapping succeeds or fails. This is safe because trigger_mapping_submit is the same reactiveVal that drives the (synchronous) mapping and strictly increments on every click, so repeated failed attempts each re-enable the button.

Definition of Done

• After an incomplete-mapping error, the user can fix the mapping and click Next again without restarting the app.
• The Next button is re-enabled after every mapping submission, on success or failure.
• No regression to the normal upload → mapping → filtering → preview flow.

How to test

1. devtools::load_all() then aNCA::run_app().
2. Upload a dataset and open the Mapping step.
3. Leave a required variable unmapped and click Next — an error notification appears (Unmapped required columns detected: ...).
4. Map the missing variable and click Next again — the button is clickable and the flow proceeds (previously: button stuck disabled, app restart required).

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)
• If any .scss change was done, run data-raw/compile_css.R
• If a package dependency was added/changed, run data-raw/test_suggests_hidden.R

Notes to reviewer

• The change is a reactive-dependency fix in Shiny module code, so there is no pure function to unit-test; please verify interactively.
• R was not available in the authoring environment, so devtools::test() and lintr::lint_package() were not run here. Line lengths were checked manually (all <=100).
• Version bumped to 0.1.0.9186.