feat: overdue highlighting, relative dates, undo write, buffer mappings (#1)

* feat(config): add category_order field

Problem: category display order was always insertion order with no way
to configure it.

Solution: add category_order to config defaults so users can declare a
preferred category ordering; unspecified categories append after.

* feat(parse): add relative date resolution

Problem: due dates required full YYYY-MM-DD input, adding friction for
common cases like "today" or "next monday".

Solution: add resolve_date() supporting today, tomorrow, +Nd, and
weekday abbreviations; extend inline token parsing to resolve relative
values before falling back to strict date validation.

* feat(views): overdue flag, category in priority view, category ordering

Problem: overdue tasks were visually indistinct from upcoming ones;
priority view had no category context; category display order was not
configurable.

Solution: compute overdue meta flag for pending tasks past their due
date; set show_category on priority view task meta; reorder categories
according to config.category_order when present.

* feat(buffer): overdue highlight, category virt text in priority view

Problem: overdue tasks had no visual distinction; priority view showed
no category context alongside due dates.

Solution: add PendingOverdue highlight group; render category name as
right-aligned virtual text in priority view, composited with the due
date when both are present.

* feat(init): undo write and buffer-local default mappings

Problem: _undo_state was captured on every save but never consumed;
toggle_priority and prompt_date had no buffer-local defaults, requiring
manual <Plug> configuration.

Solution: implement undo_write() to restore pre-save task state; add !,
d, and U as buffer-local defaults following fugitive's philosophy of
owning the buffer; expose :Pending undo as a command alias.

* test(views): add views spec

Problem: views.lua had no test coverage.

Solution: add 26 tests covering category_view and priority_view
including sort order, line format, overdue detection, show_category
meta, and category_order config behavior.

* test(archive): add archive spec

Problem: archive had no test coverage.

Solution: add 9 tests covering cutoff logic, custom day counts, pending
task preservation, deleted task cleanup, and notify output.

* docs: add vimdoc

Problem: no :help documentation existed.

Solution: add doc/pending.txt covering all features — commands,
mappings, views, configuration, Google Calendar sync, highlight groups,
data format, and health check — following standard vimdoc conventions.

* ci: format

* fix: resolve lint and type check errors

Problem: selene flagged unused variables in new spec files; LuaLS
flagged os.date/os.time return type mismatches, integer? assignments,
and stale task.Task/task.GcalConfig type references.

Solution: prefix unused spec variables with _ or drop unnecessary
assignments; add --[[@as string/integer]] casts for os.date and
os.time calls; add category_order field to pending.Config annotation;
fix task.GcalConfig -> pending.GcalConfig and task.Task[] ->
pending.Task[]; add nil guards on meta[row].id before store calls;
cast store.data() return to non-optional.

* ci: format

* fix: sync

* ci: format

lua/pending/views.lua

@@ -7,6 +7,8 @@ local config = require('pending.config')
 ---@field raw_due? string
 ---@field status? string
 ---@field category? string
+---@field overdue? boolean
+---@field show_category? boolean
 
 ---@class pending.views
 local M = {}
@@ -21,8 +23,12 @@ local function format_due(due)
   if not y then
     return due
   end
-  local t = os.time({ year = tonumber(y), month = tonumber(m), day = tonumber(d) })
-  return os.date(config.get().date_format, t)
+  local t = os.time({
+    year = tonumber(y) --[[@as integer]],
+    month = tonumber(m) --[[@as integer]],
+    day = tonumber(d) --[[@as integer]],
+  })
+  return os.date(config.get().date_format, t) --[[@as string]]
 end
 
 ---@param tasks pending.Task[]
@@ -66,6 +72,7 @@ end
 ---@return string[] lines
 ---@return pending.LineMeta[] meta
 function M.category_view(tasks)
+  local today = os.date('%Y-%m-%d') --[[@as string]]
   local by_cat = {}
   local cat_order = {}
   local cat_seen = {}
@@ -86,6 +93,24 @@ function M.category_view(tasks)
     end
   end
 
+  local cfg_order = config.get().category_order
+  if cfg_order and #cfg_order > 0 then
+    local ordered = {}
+    local seen = {}
+    for _, name in ipairs(cfg_order) do
+      if cat_seen[name] then
+        table.insert(ordered, name)
+        seen[name] = true
+      end
+    end
+    for _, name in ipairs(cat_order) do
+      if not seen[name] then
+        table.insert(ordered, name)
+      end
+    end
+    cat_order = ordered
+  end
+
   for _, cat in ipairs(cat_order) do
     sort_tasks(by_cat[cat])
     sort_tasks(done_by_cat[cat])
@@ -123,6 +148,7 @@ function M.category_view(tasks)
         raw_due = task.due,
         status = task.status,
         category = cat,
+        overdue = task.status == 'pending' and task.due ~= nil and task.due < today or nil,
       })
     end
   end
@@ -134,6 +160,7 @@ end
 ---@return string[] lines
 ---@return pending.LineMeta[] meta
 function M.priority_view(tasks)
+  local today = os.date('%Y-%m-%d') --[[@as string]]
   local pending = {}
   local done = {}
 
@@ -172,6 +199,8 @@ function M.priority_view(tasks)
       raw_due = task.due,
       status = task.status,
       category = task.category,
+      overdue = task.status == 'pending' and task.due ~= nil and task.due < today or nil,
+      show_category = true,
     })
   end