Stop a table cursor from getting stuck at -1

Assigning an on-call week panicked with "index out of range [-1]" on an
ordinary schedule. The index came from scheduleTable.Cursor().

The cursor is not ours. bubbles' SetRows clamps it down when rows shrink
(`if m.cursor > len(rows)-1`) but never back up, so setting zero rows drives it
to -1 and filling the table afterwards leaves it there -- -1 is not greater
than len-1, so nothing corrects it. Every table in this package is rebuilt from
empty exactly once, when the first WindowSizeMsg arrives before any fetch has
returned, so every cursor started at -1 and stayed there until the user pressed
up or down. Pressing a direction key first is why this was survivable at all.

setRows restores the invariant the rest of the package already assumes: a table
with rows has a usable cursor. Every rebuild goes through it.

Five call sites also bounds-checked only the top of the range, and are now
consistent with their siblings, which already had `i < 0 ||`. They were the
same latent panic: deleting a schedule entry, deleting a user, editing a topic,
opening the API key menu, and the week assignment that actually fired.

The regression test deliberately never calls SetCursor. That is what the
existing schedule tests do, and SetCursor clamps, which is exactly how this got
past them. It drives the real order instead: size, then data, then keys.

Also carries a gofmt pass, which is why untouched files appear in the diff.
The move to git.ryuvia.com rewrote import paths without re-sorting them, and
the new path sorts before github.com/charmbracelet/..., where the old one
sorted after. go vet does not look at import order, so CI had nothing to say.

main.go

@@ -5,11 +5,11 @@ import (
 	"fmt"
 	"os"
 
-	tea "github.com/charmbracelet/bubbletea"
 	"git.ryuvia.com/niklas/terdut-tui/internal/api"
 	"git.ryuvia.com/niklas/terdut-tui/internal/config"
 	"git.ryuvia.com/niklas/terdut-tui/internal/tui"
 	"git.ryuvia.com/niklas/terdut-tui/internal/updater"
+	tea "github.com/charmbracelet/bubbletea"
 )
 
 var version = "dev"