feat: persistent inline extmarks and configurable EOL format (#97)

* refactor(buffer): split extmark namespace into `ns_eol` and `ns_inline`

Problem: all extmarks shared a single `pending` namespace, making it
impossible to selectively clear position-sensitive extmarks (overlays,
highlights) while preserving stable EOL virtual text (due dates,
recurrence).

Solution: introduce `ns_eol` for end-of-line virtual text and
`ns_inline` for overlays and highlights. `clear_marks()` and
`apply_extmarks()` operate on both namespaces independently.

* feat(buffer): track line changes via `on_bytes` to keep `_meta` aligned

Problem: `_meta` is a positional array keyed by line number. Line
insertions and deletions during editing desync it from actual buffer
content, breaking `get_fold()`, cursor-based task lookups, and extmark
re-application.

Solution: attach an `on_bytes` callback that adjusts `_meta` on line
insertions/deletions and tracks dirty rows. Remove the manual
`_meta` insert from `open_line()` since `on_bytes` now handles it.
Reset dirty rows on each full render.

* feat(buffer): clear only inline extmarks on dirty rows during edits

Problem: `TextChanged` cleared all extmarks (both namespaces) on every
edit, causing EOL virtual text (due dates, recurrence) to vanish while
the user types.

Solution: replace blanket `clear_marks()` with per-row
`clear_inline_row()` that only removes `ns_inline` extmarks on rows
flagged dirty by `on_bytes`. EOL virtual text is preserved untouched.

* feat(buffer): re-apply inline extmarks after edits

Problem: inline extmarks (checkbox overlays, strikethrough, header
highlights) were cleared during edits and only restored on `:w`,
leaving the buffer visually bare while editing.

Solution: extract `apply_inline_row()` from `apply_extmarks()` and
call it via `reapply_dirty_inline()` on `InsertLeave` and normal-mode
`TextChanged`. Insert-mode `TextChangedI` still only clears inline
marks on dirty rows to avoid overlay flicker while typing.

* fix(buffer): suppress `on_bytes` during render and fix definition order

Problem: `on_bytes` fired during `render()`'s `nvim_buf_set_lines`,
corrupting `_meta` with duplicate entries and causing out-of-range
extmark errors. Also, `apply_inline_row` was defined after its first
caller `reapply_dirty_inline`.

Solution: add `_rendering` guard flag around `nvim_buf_set_lines` in
`render()` so `on_bytes` is a no-op during authoritative renders.
Move `apply_inline_row` above `reapply_dirty_inline` to satisfy Lua
local scoping rules.

* feat(buffer): add configurable `eol_format` for EOL virtual text

Problem: EOL virtual text order (category → recurrence → due) and the
double-space separator are hardcoded in `apply_extmarks()`. Users cannot
reorder, omit, or restyle metadata fields.

Solution: Add `eol_format` config field (default `'%c  %r  %d'`) with
`%c`, `%r`, `%d` specifiers. `parse_eol_format()` tokenizes the format
string; `build_eol_virt()` resolves specifiers against `LineMeta` and
collapses literals around absent fields.

* ci: format

lua/pending/buffer.lua

@@ -352,30 +352,102 @@ function M.get_fold()
   end
 end
 
+---@class pending.EolSegment
+---@field type 'specifier'|'literal'
+---@field key? 'c'|'r'|'d'
+---@field text? string
+
+---@param fmt string
+---@return pending.EolSegment[]
+local function parse_eol_format(fmt)
+  local segments = {}
+  local pos = 1
+  local len = #fmt
+  while pos <= len do
+    if fmt:sub(pos, pos) == '%' and pos + 1 <= len then
+      local key = fmt:sub(pos + 1, pos + 1)
+      if key == 'c' or key == 'r' or key == 'd' then
+        table.insert(segments, { type = 'specifier', key = key })
+        pos = pos + 2
+      else
+        table.insert(segments, { type = 'literal', text = '%' .. key })
+        pos = pos + 2
+      end
+    else
+      local next_pct = fmt:find('%%', pos + 1)
+      local chunk = next_pct and fmt:sub(pos, next_pct - 1) or fmt:sub(pos)
+      table.insert(segments, { type = 'literal', text = chunk })
+      pos = pos + #chunk
+    end
+  end
+  return segments
+end
+
+---@param segments pending.EolSegment[]
+---@param m pending.LineMeta
+---@param icons pending.Icons
+---@return string[][]
+local function build_eol_virt(segments, m, icons)
+  local due_hl = m.overdue and 'PendingOverdue' or 'PendingDue'
+  local resolved = {}
+  for i, seg in ipairs(segments) do
+    if seg.type == 'specifier' then
+      local text, hl
+      if seg.key == 'c' and m.show_category and m.category then
+        text = icons.category .. ' ' .. m.category
+        hl = 'PendingHeader'
+      elseif seg.key == 'r' and m.recur then
+        text = icons.recur .. ' ' .. m.recur
+        hl = 'PendingRecur'
+      elseif seg.key == 'd' and m.due then
+        text = icons.due .. ' ' .. m.due
+        hl = due_hl
+      end
+      resolved[i] = text and { text = text, hl = hl, present = true } or { present = false }
+    else
+      resolved[i] = { text = seg.text, hl = 'Normal', literal = true }
+    end
+  end
+
+  local virt_parts = {}
+  for i, r in ipairs(resolved) do
+    if r.literal then
+      local prev_present, next_present = false, false
+      for j = i - 1, 1, -1 do
+        if not resolved[j].literal then
+          prev_present = resolved[j].present
+          break
+        end
+      end
+      for j = i + 1, #resolved do
+        if not resolved[j].literal then
+          next_present = resolved[j].present
+          break
+        end
+      end
+      if prev_present and next_present then
+        table.insert(virt_parts, { r.text, r.hl })
+      end
+    elseif r.present then
+      table.insert(virt_parts, { r.text, r.hl })
+    end
+  end
+  return virt_parts
+end
+
 ---@param bufnr integer
 ---@param line_meta pending.LineMeta[]
 local function apply_extmarks(bufnr, line_meta)
-  local icons = config.get().icons
+  local cfg = config.get()
+  local icons = cfg.icons
+  local eol_segments = parse_eol_format(cfg.eol_format or '%c  %r  %d')
   vim.api.nvim_buf_clear_namespace(bufnr, ns_eol, 0, -1)
   vim.api.nvim_buf_clear_namespace(bufnr, ns_inline, 0, -1)
   for i, m in ipairs(line_meta) do
     local row = i - 1
     if m.type == 'task' then
-      local due_hl = m.overdue and 'PendingOverdue' or 'PendingDue'
-      local virt_parts = {}
-      if m.show_category and m.category then
-        table.insert(virt_parts, { icons.category .. ' ' .. m.category, 'PendingHeader' })
-      end
-      if m.recur then
-        table.insert(virt_parts, { icons.recur .. ' ' .. m.recur, 'PendingRecur' })
-      end
-      if m.due then
-        table.insert(virt_parts, { icons.due .. ' ' .. m.due, due_hl })
-      end
+      local virt_parts = build_eol_virt(eol_segments, m, icons)
       if #virt_parts > 0 then
-        for p = 1, #virt_parts - 1 do
-          virt_parts[p][1] = virt_parts[p][1] .. '  '
-        end
         vim.api.nvim_buf_set_extmark(bufnr, ns_eol, row, 0, {
           virt_text = virt_parts,
           virt_text_pos = 'eol',