docs: describe 3-level help paste hierarchy

USAGE.md: add Detailed Help section with format example.
CHEATSHEET.md: note hierarchy layout in help description.
TASKS.md: update sprint with hierarchy task and test count.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/USAGE.md

@@ -206,6 +206,30 @@ unchanged. The server name is derived from the hostname automatically.
 | `!cron <add\|del\|list>` | Scheduled command execution (admin) |
 | `!webhook` | Show webhook listener status (admin) |
 
+### Detailed Help (FlaskPaste)
+
+`!help` pastes detailed reference output to FlaskPaste and appends the
+URL. The paste uses a 3-level indentation hierarchy:
+
+```
+[plugin-name]
+    Plugin description.
+
+    !command -- short help
+        Full docstring with usage, subcommands,
+        and examples.
+
+    !other -- another command
+        Its docstring here.
+```
+
+- `!help` (no args) -- pastes the full reference grouped by plugin
+- `!help <cmd>` -- pastes the command's docstring (command at column 0)
+- `!help <plugin>` -- pastes all commands under the plugin header
+
+If FlaskPaste is not loaded or the paste fails, the short IRC reply
+still works -- no regression.
+
 ### Command Shorthand
 
 Commands can be abbreviated to any unambiguous prefix: