docs: align engine terminology in telegram and docs (#162)

docs/how-to/switch-engines.md

@@ -29,7 +29,7 @@ Use `/agent`:
 - In normal chats, it affects the whole chat.
 - In group chats, only admins can change defaults.
 
-Selection precedence (highest to lowest): resume token → `/engine` directive → topic default → chat default → project default → global default.
+Selection precedence (highest to lowest): resume token → `/<engine-id>` directive → topic default → chat default → project default → global default.
 
 ## Engine installation
 
@@ -40,4 +40,3 @@ Takopi shells out to engine CLIs. Install them and make sure they’re on your `
 
 - [Commands & directives](../reference/commands-and-directives.md)
 - [Config reference](../reference/config.md)
-

docs/how-to/topics.md

@@ -1,6 +1,6 @@
 # Topics
 
-Topics bind Telegram **forum threads** to a project/branch context. Each topic keeps its own session and default agent, which is ideal for teams or multi-project work.
+Topics bind Telegram **forum threads** to a project/branch context. Each topic keeps its own session and default engine, which is ideal for teams or multi-project work.
 
 !!! tip "Workspace workflow"
     If you chose the **workspace** workflow during [onboarding](../tutorials/install.md), topics are already enabled. This guide covers advanced topic configuration and usage.
@@ -9,7 +9,7 @@ Topics bind Telegram **forum threads** to a project/branch context. Each topic k
 
 - Keep each thread tied to a repo + branch
 - Avoid context collisions in busy team chats
-- Set a default agent per topic with `/agent set`
+- Set a default engine per topic with `/agent set`
 
 ## Requirements checklist
 
@@ -76,7 +76,7 @@ Note: Outside topics (private chats or main group chats), `/ctx` binds the chat
 
 Use `/new` inside the topic to clear stored sessions for that thread.
 
-## Set a default agent per topic
+## Set a default engine per topic
 
 Use `/agent set` inside the topic:
 

docs/how-to/worktrees.md

@@ -44,7 +44,7 @@ echo ".worktrees/" >> ~/.config/git/ignore
 ## Context persistence
 
 When project/worktree context is active, Takopi includes a `ctx:` footer in messages.
-When you reply, this context carries forward (you usually don’t need to repeat `/project @branch`).
+When you reply, this context carries forward (you usually don’t need to repeat `/<project-alias> @branch`).
 
 ## Related
 

docs/how-to/write-a-plugin.md

@@ -24,7 +24,9 @@ mytransport = "mytransport.backend:BACKEND"
 mycommand = "mycommand.backend:BACKEND"
 ```
 
-## Engine backend plugin (runner)
+## Engine backend plugin
+
+An engine backend builds a `Runner` via `build_runner(...)`.
 
 Minimal example: