fix(parse): skip forge refs in right-to-left metadata scan

Problem: `parse.body()` scans tokens right-to-left and breaks on the
first non-metadata token. Forge refs like `gl:a/b#12` halted the scan,
preventing metadata tokens to their left (e.g. `due:tomorrow`) from
being parsed. Additionally, `diff.parse_buffer()` ignored
`metadata.priority` from `+!!` tokens and only used checkbox-derived
priority, and priority updates between two non-zero values were silently
skipped.

Solution: Recognize forge ref tokens via `forge.parse_ref()` during the
right-to-left scan and skip past them, re-appending them to the
description so `forge.find_refs()` still works. Prefer
`metadata.priority` over checkbox priority in `parse_buffer()`, and
simplify the priority update condition to catch all value changes.

spec/diff_spec.lua

@@ -379,5 +379,41 @@ describe('diff', function()
       local task = s:get(1)
       assert.are.equal(0, task.priority)
     end)
+
+    it('sets priority from +!! token', function()
+      local lines = {
+        '# Inbox',
+        '- [ ] Pay bills +!!',
+      }
+      diff.apply(lines, s)
+      s:load()
+      local task = s:get(1)
+      assert.are.equal(2, task.priority)
+    end)
+
+    it('updates priority between non-zero values', function()
+      s:add({ description = 'Task name', priority = 2 })
+      s:save()
+      local lines = {
+        '# Inbox',
+        '/1/- [!] Task name',
+      }
+      diff.apply(lines, s)
+      s:load()
+      local task = s:get(1)
+      assert.are.equal(1, task.priority)
+    end)
+
+    it('parses metadata with forge ref on same line', function()
+      local lines = {
+        '# Inbox',
+        '- [ ] Fix bug due:2026-03-15 gh:user/repo#42',
+      }
+      diff.apply(lines, s)
+      s:load()
+      local task = s:get(1)
+      assert.are.equal('2026-03-15', task.due)
+      assert.is_not_nil(task._extra._forge_ref)
+    end)
   end)
 end)