docs: document wip and blocked task states (#99)

Problem: The vimdoc only describes `pending`/`done`/`deleted` statuses
with no mention of work-in-progress or blocked states.

Solution: Document new `wip` and `blocked` statuses across views (sort
order), filters (new predicates), icons (`>` and `=`), highlight groups
(`PendingWip`, `PendingBlocked`), and the data format schema.

doc/pending.txt

@@ -396,14 +396,14 @@ Category view (default): ~                             *pending-view-category*
     Tasks are grouped under their category header. Categories appear in the
     order tasks were added unless `category_order` is set (see
     |pending-config|). Blank lines separate categories. Within each category,
-    pending tasks appear before done tasks. Priority tasks (`!`) are sorted
-    first within each group. Category sections are foldable with `zc` and
-    `zo`.
+    tasks are sorted by status (wip → pending → blocked → done), then by
+    priority, then by insertion order. Category sections are foldable with
+    `zc` and `zo`.
 
 Queue view: ~                                             *pending-view-queue*
-    A flat list of all tasks sorted by priority, then by due date (tasks
-    without a due date sort last), then by internal order. Done tasks appear
-    after all pending tasks. Category names are shown as right-aligned virtual
+    A flat list of all tasks sorted by status (wip → pending → blocked →
+    done), then by priority, then by due date (tasks without a due date sort
+    last), then by internal order. Category names are shown as right-aligned virtual
     text alongside the due date virtual text so tasks remain identifiable
     across categories. The buffer is named `pending://queue`.
 
@@ -435,6 +435,10 @@ Available predicates: ~
 
     `priority`    Show only tasks with priority > 0 (the `!` marker).
 
+    `wip`         Show only tasks with status `wip` (work in progress).
+
+    `blocked`     Show only tasks with status `blocked`.
+
     `clear`       Special value for |:Pending-filter| — clears the active filter
               and shows all tasks.
 
@@ -767,14 +771,16 @@ Fields: ~
 
     {icons}              (table)                          *pending.Icons*
                          Icon characters displayed in the buffer. The
-                         {pending}, {done}, and {priority} characters
-                         appear inside brackets (`[icon]`) as an overlay
-                         on the checkbox. The {category} character
-                         prefixes both header lines and EOL category
-                         labels. Fields:
+                         {pending}, {done}, {priority}, {wip}, and
+                         {blocked} characters appear inside brackets
+                         (`[icon]`) as an overlay on the checkbox. The
+                         {category} character prefixes both header lines
+                         and EOL category labels. Fields:
                            {pending}   Pending task character. Default: ' '
                            {done}      Done task character. Default: 'x'
                            {priority}  Priority task character. Default: '!'
+                           {wip}       Work-in-progress character. Default: '>'
+                           {blocked}   Blocked task character. Default: '='
                            {due}       Due date prefix. Default: '.'
                            {recur}     Recurrence prefix. Default: '~'
                            {category}  Category prefix. Default: '#'
@@ -823,6 +829,14 @@ PendingOverdue      Applied to the due date virtual text of overdue tasks.
 PendingDone         Applied to the text of completed tasks.
                     Default: links to `Comment`.
 
+                                                                 *PendingWip*
+PendingWip          Applied to the checkbox icon of work-in-progress tasks.
+                    Default: links to `DiagnosticInfo`.
+
+                                                             *PendingBlocked*
+PendingBlocked      Applied to the checkbox icon and text of blocked tasks.
+                    Default: links to `DiagnosticError`.
+
                                                             *PendingPriority*
 PendingPriority     Applied to the `! ` priority marker on priority tasks.
                     Default: links to `DiagnosticWarn`.
@@ -1188,7 +1202,8 @@ Schema: >
 Task fields: ~
     {id}          (integer) Unique, auto-incrementing task identifier.
     {description} (string)  Task text as shown in the buffer.
-    {status}      (string)  `'pending'`, `'done'`, or `'deleted'`.
+    {status}      (string)  `'pending'`, `'wip'`, `'blocked'`, `'done'`,
+                            or `'deleted'`.
     {category}    (string)  Category name. Defaults to `default_category`.
     {priority}    (integer) `1` for priority tasks, `0` otherwise.
     {due}         (string)  ISO date string `YYYY-MM-DD`, or absent.