docs(textobj): add mini.ai integration recipe to vimdoc

Problem: users with mini.ai installed find that buffer-local `at`, `it`,
`aC`, `iC` text objects never fire because mini.ai intercepts `a`/`i` as
single-key handlers in operator-pending/visual modes before Neovim's
mapping system can route them to buffer-local maps.

Solution: add a *pending-mini-ai* recipe section to the RECIPES block in
pending.txt. The recipe explains the conflict, describes mini.ai's
custom_textobjects spec (`{ from = {line,col}, to = {line,col} }`), and
shows how to wrap `textobj.inner_task_range` and `textobj.category_bounds`
(the two functions that return positional data) into the shape mini.ai
expects, registered via `vim.b.miniai_config` in a FileType autocmd. Notes
that `aC` cannot be expressed this way due to its linewise selection, and
that the built-in keymaps work fine for users without mini.ai.

doc/pending.txt

@@ -644,6 +644,77 @@ Event-driven statusline refresh: >lua
     })
 <
 
+mini.ai integration: ~                                        *pending-mini-ai*
+mini.ai (from mini.nvim) maps `a` and `i` as single-key handlers in
+operator-pending and visual modes. It captures the next keystroke internally
+rather than routing it through Neovim's mapping system, which means the
+buffer-local `at`, `it`, `aC`, and `iC` maps never fire for users who have
+mini.ai installed.
+
+The fix is to register pending.nvim's text objects as mini.ai custom
+textobjects via `vim.b.miniai_config` in a `FileType` autocmd. mini.ai's
+`custom_textobjects` spec expects each entry to be a function returning
+`{ from = { line, col }, to = { line, col } }` (1-indexed, col is
+byte-offset from 1).
+
+pending.nvim's `textobj.inner_task_range(line)` returns the start and end
+column offsets within the current line. Combine it with the cursor row and
+the buffer line to build the region tables mini.ai expects: >lua
+
+    vim.api.nvim_create_autocmd('FileType', {
+      pattern = 'pending',
+      callback = function()
+        local function task_inner()
+          local textobj = require('pending.textobj')
+          local row = vim.api.nvim_win_get_cursor(0)[1]
+          local line = vim.api.nvim_buf_get_lines(0, row - 1, row, false)[1]
+          if not line then return end
+          local s, e = textobj.inner_task_range(line)
+          if s > e then return end
+          return { from = { line = row, col = s }, to = { line = row, col = e } }
+        end
+
+        local function category_inner()
+          local textobj = require('pending.textobj')
+          local buffer = require('pending.buffer')
+          local meta = buffer.meta()
+          if not meta then return end
+          local row = vim.api.nvim_win_get_cursor(0)[1]
+          local header_row, last_row = textobj.category_bounds(row, meta)
+          if not header_row then return end
+          local first_task, last_task
+          for r = header_row + 1, last_row do
+            if meta[r] and meta[r].type == 'task' then
+              if not first_task then first_task = r end
+              last_task = r
+            end
+          end
+          if not first_task then return end
+          local first_line = vim.api.nvim_buf_get_lines(0, first_task - 1, first_task, false)[1] or ''
+          local last_line = vim.api.nvim_buf_get_lines(0, last_task - 1, last_task, false)[1] or ''
+          return {
+            from = { line = first_task, col = 1 },
+            to   = { line = last_task,  col = #last_line },
+          }
+        end
+
+        vim.b.miniai_config = {
+          custom_textobjects = { t = task_inner, C = category_inner },
+        }
+      end,
+    })
+<
+
+Note that the default `keymaps.a_task = 'at'` and friends still work in
+standard Neovim operator-pending mode for users who do not have mini.ai. The
+`vim.b.miniai_config` block is only needed when mini.ai is active.
+
+`aC` (outer category) is not exposed here because mini.ai does not support
+the linewise selection that `aC` requires. Use the buffer-local `aC` key
+directly, or disable `a_category` in `keymaps` and handle it via a
+`vim.b.miniai_config` entry that returns a linewise region if mini.ai's
+spec allows it in your version.
+
 ==============================================================================
 GOOGLE CALENDAR                                                 *pending-gcal*