Act on the selected row, not the one the table moved to

In Users, pressing k on a user opened API keys for the user above it.
The dashboard hands every key to the section's table before the
section's own handler reads the cursor, and bubbles' table claims
several letters for navigation: k is up, d half a page down, f a page
down. A letter that is also an action therefore moved the cursor first,
and the action landed on the row it had moved to. With your own user
first in the list, k looked like it only ever showed your own keys.

The same collision hit two destructive keys:

- d in Users asked to delete a user half a page below the selected one.
  The confirmation names the user, and that was the only thing standing
  between a keypress and deleting the wrong person.
- d in Schedule targeted a different day's assignment the same way.

f in Incidents and Alerts cycled the filter and paged the cursor down
too, which was harmless but wrong.

Each table now gives up exactly the letters its section acts on,
through tableKeyMap. The arrow keys and every other default binding are
untouched. The cost is that k no longer moves up in Users, where it
means API keys, as the README has always said. The up arrow still
works, and the README now says to use it there.

users_test.go reproduces all four. With tableKeyMap reverted to the
defaults, each of them fails exactly as reported.

internal/tui/users_test.go

@@ -0,0 +1,84 @@
+package tui
+
+import (
+	"testing"
+	"time"
+
+	"git.ryuvia.com/niklas/terdut-tui/internal/api"
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+// threeUsers is the Users section with the cursor on the last of three users.
+func threeUsers() Model {
+	m := onUsers([]api.User{
+		{ID: 1, Username: "niklas"},
+		{ID: 2, Username: "anna"},
+		{ID: 3, Username: "erik"},
+	})
+	m.userManageTable.SetCursor(2)
+	return m
+}
+
+// The table used to see k before the section did, take it as "up", and the
+// handler then opened API keys for the user above the one selected.
+func TestUsers_APIKeysOpenForTheSelectedUser(t *testing.T) {
+	m, _ := press(t, threeUsers(), "k")
+	if m.mode != modeAPIKeyMenu {
+		t.Fatalf("expected the API key menu, got mode %v", m.mode)
+	}
+	if m.selectedUser.Username != "erik" {
+		t.Errorf("API keys opened for %s, want erik", m.selectedUser.Username)
+	}
+}
+
+// Same collision with d, which the table read as half a page down: the delete
+// confirmation named a different user than the one under the cursor.
+func TestUsers_DeleteTargetsTheSelectedUser(t *testing.T) {
+	m := threeUsers()
+	m.userManageTable.SetCursor(0)
+	m, _ = press(t, m, "d")
+	if m.mode != modeConfirm || m.selectedUser.Username != "niklas" {
+		t.Errorf("delete asked about %q in mode %v, want niklas", m.selectedUser.Username, m.mode)
+	}
+}
+
+func TestSchedule_DeleteTargetsTheSelectedDay(t *testing.T) {
+	m := sized()
+	m.activeSection = sectionSchedule
+	m.scheduleEntries = []api.ScheduleEntry{
+		{ID: 10, UserID: 1, Username: "niklas", Date: m.scheduleWindow.Format("2006-01-02")},
+		{ID: 11, UserID: 2, Username: "anna", Date: m.scheduleWindow.AddDate(0, 0, 1).Format("2006-01-02")},
+	}
+	m.scheduleDays = buildScheduleDays(m.scheduleWindow, m.scheduleEntries)
+	m.rebuildScheduleTable()
+	m.scheduleTable.SetCursor(0)
+	m, _ = press(t, m, "d")
+	if m.pendingDeleteEntry == nil || m.pendingDeleteEntry.ID != 10 {
+		t.Errorf("schedule delete targeted %+v, want entry 10", m.pendingDeleteEntry)
+	}
+}
+
+// f cycles the filter; it must not also page the cursor down.
+func TestFilter_DoesNotMoveTheCursor(t *testing.T) {
+	m := sized()
+	m.incidents = make([]api.Incident, 40)
+	for i := range m.incidents {
+		m.incidents[i] = api.Incident{ID: int64(i + 1), Title: "x", Status: api.StatusTriggered, TriggeredAt: time.Now()}
+	}
+	m.rebuildIncidentTable()
+	m, _ = press(t, m, "f")
+	if c := m.incidentTable.Cursor(); c != 0 {
+		t.Errorf("f moved the cursor to %d", c)
+	}
+}
+
+// The arrow keys still move the users table, now that k is an action there.
+func TestUsers_ArrowKeysStillNavigate(t *testing.T) {
+	m := threeUsers()
+	next, _ := m.Update(keyUp())
+	if c := next.(Model).userManageTable.Cursor(); c != 1 {
+		t.Errorf("up arrow left the cursor on %d, want 1", c)
+	}
+}
+
+func keyUp() tea.KeyMsg { return tea.KeyMsg{Type: tea.KeyUp} }