fix(git): validate placement, cache repo lookups, tighten lifecycle

lua/git/status_view.lua

@@ -49,7 +49,7 @@ end
 local state = {}
 
 local group =
-    vim.api.nvim_create_augroup("ow.git.status_win", { clear = false })
+    vim.api.nvim_create_augroup("ow.git.status_win", { clear = true })
 local ns = vim.api.nvim_create_namespace("ow.git.status_win")
 
 ---@return integer? win
@@ -713,6 +713,14 @@ end
 function M.open(opts)
     opts = opts or {}
     local placement = opts.placement or "sidebar"
+    if not vim.tbl_contains(M.PLACEMENTS, placement) then
+        util.error(
+            "invalid placement: %s (expected one of %s)",
+            placement,
+            table.concat(M.PLACEMENTS, ", ")
+        )
+        return
+    end
     local r = repo.resolve()
     if not r then
         util.error("not in a git repository")