feat: complete task editing coverage (#109)

Problem: the task editing surface had gaps — category and recurrence had
no keymaps, `:Pending edit` required knowing the task ID, tasks couldn't
be reordered with a keymap, priority was binary (0/1), and `wip`/`blocked`
states were documented but unimplemented.

Solution: fill every cell so every property is editable in every way.

- `gc`/`gr` keymaps for category select and recurrence prompt
- cursor-aware `:Pending edit` (omit ID to use task under cursor)
- `J`/`K` keymaps to reorder tasks within a category
- multi-level priorities (`max_priority` config, `g!` cycles 0→1→2→3→0)
- `+!!`/`+!!!` tokens in `:Pending edit`, `:Pending add`, `parse.body()`
- `PendingPriority2`/`PendingPriority3` highlight groups
- `gw`/`gb` keymaps toggle `wip`/`blocked` status
- `>`/`=` state chars in buffer rendering and diff parsing
- `PendingWip`/`PendingBlocked` highlight groups
- sort order: wip → pending → blocked → done
- `wip`/`blocked` filter predicates and icons

lua/pending/store.lua

@@ -3,7 +3,7 @@ local config = require('pending.config')
 ---@class pending.Task
 ---@field id integer
 ---@field description string
----@field status 'pending'|'done'|'deleted'
+---@field status 'pending'|'done'|'deleted'|'wip'|'blocked'
 ---@field category? string
 ---@field priority integer
 ---@field due? string