Power User dashboard: implement real Fremdbewertung overview + add missing comparison PDF handler

[Copilot]

Power User TAB 7 (Fremdbewertung) was still wired to demo-only UI and did not expose project-scoped Fremdbewertung data. This PR aligns the Power User experience with the existing admin Fremdbewertung overview and adds the missing server-side handler for the already-rendered poweruser_download_comparison button.

• TAB 7 UI replacement (demo → data-backed overview)

  • Replaced warning/placeholder content with a full overview layout:
    • poweruser_fremd_project project selector
    • poweruser_fremdbewertung_summary summary cards
    • reviewer/section filters (poweruser_fremd_filter_user, poweruser_fremd_filter_section) + refresh button
    • poweruser_fremdbewertung_table DT output
    • poweruser_download_fremdbewertung_csv export button

• Power User project dropdown wiring

  • Extended the existing get_all_projects()-driven updateSelectInput(...) block inside the Power User role observer to also populate poweruser_fremd_project.

• Power User Fremdbewertung server logic

  • Added poweruser_fremdbewertung_summary (renderUI) with project-scoped counts:
    • distinct reviewers
    • total responses
  • Added poweruser_fremdbewertung_data reactive using the required DB query shape and optional filters:
    • reviewer exact match
    • section prefix match (question_id LIKE 'X%')
  • Added poweruser_fremdbewertung_table (renderDataTable) over the reactive dataset.
  • Added project-scoped reviewer-choice refresh for poweruser_fremd_filter_user.
  • Added poweruser_download_fremdbewertung_csv (downloadHandler) exporting the same filtered dataset.

• Missing comparison download handler

  • Implemented output$poweruser_download_comparison <- downloadHandler(...) in the Power User server section, next to other Power User report downloads.
  • Handler resolves project title from input$poweruser_report_project, generates Vergleichstabelle_<Projekt>_<date>.pdf, and calls generate_comparison_pdf(file, project_id, user_role()).

output$poweruser_download_comparison <- downloadHandler(
  filename = function() {
    project_id <- input$poweruser_report_project
    project_title <- tryCatch({
      get_all_projects() %>%
        dplyr::filter(id == as.integer(project_id)) %>%
        dplyr::pull(title)
    }, error = function(e) "Projekt")
    paste0("Vergleichstabelle_", gsub(" ", "_", project_title), "_", Sys.Date(), ".pdf")
  },
  content = function(file) {
    req(input$poweruser_report_project)
    project_id <- input$poweruser_report_project
    if (is.null(project_id) || project_id == "") return(NULL)
    generate_comparison_pdf(file, project_id, user_role())
  }
)

Original prompt

Problem

Two fixes are needed in the Power User dashboard inside app.R:

---

Fix 1 — Fremdbewertung tab (TAB 7 in poweruser_tabs)

Currently TAB 7 ("Fremdbewertung") in the power user dashboard only shows a demo warning banner and a uiOutput("poweruser_fremdbewertung_ui") placeholder. It does not show real project data.

Required change:

Replace the demo content with a fully functional Fremdbewertung overview that mirrors the existing admin fremdbewertungen tabItem. Specifically:

1. Add a project dropdown selector (selectInput("poweruser_fremd_project", ...)) at the top of the tab — populated from get_all_projects() inside the power user observeEvent(user_role(), ...) block.
2. Show a summary cards row: uiOutput("poweruser_fremdbewertung_summary").
3. Show filter dropdowns for reviewer (selectInput("poweruser_fremd_filter_user", ...)) and section (selectInput("poweruser_fremd_filter_section", ...)) plus a refresh button.
4. Show a DT table DT::dataTableOutput("poweruser_fremdbewertung_table") with actual data from the DB.
5. Add a CSV export button: downloadButton("poweruser_download_fremdbewertung_csv", ...).

In the server logic (inside observeEvent(user_role(), { if (user_role() == "power_user") { ... } })) add:

• Populate poweruser_fremd_project dropdown from get_all_projects() (add to the existing observe({ ... updateSelectInput ... }) block).
• output$poweruser_fremdbewertung_summary — render summary cards (count of reviewers, count of responses) for the selected project, similar in style to fremdbewertung_summary but scoped to input$poweruser_fremd_project.
• output$poweruser_fremdbewertung_table — renderDT that queries:

  SELECT 
    u.username as reviewer,
    r.question_id,
    r.response_value,
    r.assessment_type,
    TO_CHAR(r.submitted_at AT TIME ZONE 'Europe/Berlin', 'DD.MM.YYYY HH24:MI') as submitted_at
  FROM responses r
  JOIN users u ON u.id = r.user_id
  WHERE r.project_id = $1
    AND r.assessment_type = 'fremdbewertung'
  ORDER BY u.username, r.question_id

  filtered by input$poweruser_fremd_project, and optionally by input$poweruser_fremd_filter_user and input$poweruser_fremd_filter_section (question_id LIKE section%).
• After loading data, update poweruser_fremd_filter_user choices from unique reviewers.
• output$poweruser_download_fremdbewertung_csv — downloadHandler that exports the same data as a CSV.

---

Fix 2 — Missing poweruser_download_comparison download handler

In the UI there is already a download button:

downloadButton(
  "poweruser_download_comparison",
  "Vergleichstabelle herunterladen (Selbst- Vs. Fremdbewertung)",
  class = "btn-info",
  icon = icon("table")
)

But there is no corresponding downloadHandler in the server logic for the power user role. The existing output$download_comparison_pdf handler exists only for admin/leading_peer role.

Required change:

Inside observeEvent(user_role(), { if (user_role() == "power_user") { ... } }), add:

output$poweruser_download_comparison <- downloadHandler(
  filename = function() {
    project_id <- input$poweruser_report_project
    project_title <- tryCatch({
      get_all_projects() %>%
        dplyr::filter(id == as.integer(project_id)) %>%
        dplyr::pull(title)
    }, error = function(e) "Projekt")
    paste0("Vergleichstabelle_", gsub(" ", "_", project_title), "_", Sys.Date(), ".pdf")
  },
  content = function(file) {
    req(input$poweruser_report_project)
    project_id <- input$poweruser_report_project
    if (is.null(project_id) || project_id == "") {
      showNotification("Kein Projekt ausgewählt!", type = "error", duration = 5)
      return(NULL)
    }
    generate_comparison_pdf(file, project_id, user_role())
  }
)

Place this handler alongside the other poweruser_download_* handlers (near poweruser_download_zusammenfassung, poweruser_download_labinfo, etc.).

---

Important notes

• All changes are inside app.R.
• Do NOT break any existing functionality.
• Follow the same coding style and patterns already used in the file.
• The get_all_projects() reactive and con DB connection are already available inside the power user observeEvent block.

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