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

docs/explanation/architecture.md

@@ -165,7 +165,7 @@ sequenceDiagram
         Command->>RunnerBridge: run_one/run_many (optional)
         RunnerBridge->>Telegram: Send progress/final
     else Default routing
-        Bridge->>Bridge: Parse directives<br/>(/engine, /project, @branch)
+        Bridge->>Bridge: Parse directives<br/>(/&lt;engine-id&gt;, /&lt;project-alias&gt;, @branch)
         Bridge->>Bridge: Extract resume token<br/>from reply
         Bridge->>Bridge: Resolve worktree<br/>(if @branch)
 

docs/explanation/plugin-system.md

@@ -72,7 +72,7 @@ This lets you:
 
 ## IDs and collisions
 
-Entrypoint names become plugin IDs and appear in user-facing surfaces (CLI subcommands, Telegram commands, `/engine` directives).
+Entrypoint names become plugin IDs and appear in user-facing surfaces (CLI subcommands, Telegram commands, `/<engine-id>` directives).
 Takopi validates IDs and rejects collisions with reserved names.
 
 Plugin IDs must match:

docs/explanation/routing-and-sessions.md

@@ -27,7 +27,7 @@ Reply-to-continue works even if topics or chat sessions are enabled.
 
 For each message, Takopi:
 
-- parses directive prefixes (`/engine`, `/project`, `@branch`) from the first non-empty line
+- parses directive prefixes (`/<engine-id>`, `/<project-alias>`, `@branch`) from the first non-empty line
 - attempts to extract a resume token by polling available runners
 - if a resume token is found, routes to the matching runner; otherwise uses the configured default engine