feat(init): warn on dirty buffer before store-dependent actions

Problem: `toggle_complete`, `toggle_priority`, `prompt_date`, and
`done` (no-args) all read from `buffer.meta()` which is stale whenever
the buffer has unsaved edits, leading to silent no-ops or acting on the
wrong task.

Solution: Add a `require_saved()` guard that emits a `log.warn` and
returns false when the buffer is modified. Each store-dependent action
calls it before touching meta or the store.

lua/pending/init.lua

@@ -83,6 +83,16 @@ local function _save_and_notify()
   M._recompute_counts()
 end
 
+---@return boolean
+local function require_saved()
+  local bufnr = buffer.bufnr()
+  if bufnr and vim.bo[bufnr].modified then
+    log.warn('Unsaved changes — :w first.')
+    return false
+  end
+  return true
+end
+
 ---@return pending.Counts
 function M.counts()
   if not _counts then
@@ -388,6 +398,9 @@ function M.toggle_complete()
   if not bufnr then
     return
   end
+  if not require_saved() then
+    return
+  end
   local row = vim.api.nvim_win_get_cursor(0)[1]
   local meta = buffer.meta()
   if not meta[row] or meta[row].type ~= 'task' then
@@ -435,6 +448,9 @@ end
 function M.done(id_str)
   local id
   if not id_str or id_str == '' then
+    if not require_saved() then
+      return
+    end
     local row = vim.api.nvim_win_get_cursor(0)[1]
     local meta = buffer.meta()
     if not meta[row] or meta[row].type ~= 'task' then
@@ -443,7 +459,6 @@ function M.done(id_str)
     end
     id = meta[row].id
     if not id then
-      log.error('Task has no ID — save the buffer first.')
       return
     end
   else
@@ -493,6 +508,9 @@ function M.toggle_priority()
   if not bufnr then
     return
   end
+  if not require_saved() then
+    return
+  end
   local row = vim.api.nvim_win_get_cursor(0)[1]
   local meta = buffer.meta()
   if not meta[row] or meta[row].type ~= 'task' then
@@ -525,6 +543,9 @@ function M.prompt_date()
   if not bufnr then
     return
   end
+  if not require_saved() then
+    return
+  end
   local row = vim.api.nvim_win_get_cursor(0)[1]
   local meta = buffer.meta()
   if not meta[row] or meta[row].type ~= 'task' then