fix(terminal): offer Pi's, Oh My Pi's, Prime Agent's and Grok Build's commands

All four take typed slash commands, but the composer knew none of them:
`/` opened no menu and the placeholder offered only `@` files. List each
one's everyday commands as its installed version names them — Pi 0.99,
Oh My Pi 18.4 (`/exit`, `/retry`, `/todo`), Prime Agent 0.9 (`/effort`
rather than Pi's `/thinking`) and Grok Build 1.0 (`/mcps`, `/recap`).

src/terminal/composer.rs

@@ -731,6 +731,70 @@ fn builtin_commands(agent: CLIAgent) -> &'static [(&'static str, &'static str)]
             ("/mcp", "Show MCP server status"),
             ("/help", "Show available commands and shortcuts"),
         ],
+        CLIAgent::Pi => &[
+            ("/model", "Select model"),
+            ("/thinking", "Set thinking level"),
+            ("/compact", "Compact the session context"),
+            ("/new", "Start a new session"),
+            ("/resume", "Resume a different session"),
+            ("/tree", "Navigate the session tree"),
+            ("/fork", "Fork from a previous message"),
+            ("/session", "Show session info and stats"),
+            ("/copy", "Copy the last agent message"),
+            ("/export", "Export the session"),
+            ("/settings", "Open settings"),
+            ("/reload", "Reload extensions, skills and prompts"),
+            ("/hotkeys", "Show keyboard shortcuts"),
+            ("/quit", "Quit Pi"),
+        ],
+        CLIAgent::OhMyPi => &[
+            ("/model", "Switch model"),
+            ("/plan", "Toggle plan mode"),
+            ("/compact", "Compact the session context"),
+            ("/new", "Start a new session"),
+            ("/resume", "Resume a different session"),
+            ("/retry", "Retry the last failed turn"),
+            ("/tree", "Navigate the session tree"),
+            ("/fork", "Fork from a previous message"),
+            ("/context", "Show context usage"),
+            ("/usage", "Show provider usage and limits"),
+            ("/todo", "View or change the todo list"),
+            ("/copy", "Copy text from the conversation"),
+            ("/settings", "Open settings"),
+            ("/exit", "Exit Oh My Pi"),
+        ],
+        CLIAgent::PrimeAgent => &[
+            ("/model", "Switch model"),
+            ("/effort", "Set reasoning effort"),
+            ("/compact", "Compact the session context"),
+            ("/new", "Start a new session"),
+            ("/resume", "Resume a session"),
+            ("/tree", "Jump to any point in the session"),
+            ("/fork", "Fork from a previous message"),
+            ("/usage", "Show token, cost and context usage"),
+            ("/btw", "Ask a side question"),
+            ("/copy", "Copy the last assistant message"),
+            ("/export", "Export the session to HTML"),
+            ("/settings", "Open settings"),
+            ("/reload", "Reload extensions, skills and prompts"),
+            ("/quit", "Quit Prime Agent"),
+        ],
+        CLIAgent::Grok => &[
+            ("/model", "Switch the active model"),
+            ("/effort", "Set reasoning effort"),
+            ("/plan", "Enter plan mode"),
+            ("/compact", "Compact conversation history"),
+            ("/new", "Start a new session"),
+            ("/resume", "Resume a previous session"),
+            ("/context", "View context usage"),
+            ("/usage", "View usage"),
+            ("/btw", "Ask a side question"),
+            ("/recap", "Summarize the session so far"),
+            ("/copy", "Copy the last response"),
+            ("/mcps", "Show MCP server status"),
+            ("/settings", "Open settings"),
+            ("/quit", "Quit Grok Build"),
+        ],
         // Amp has no typed commands: `/` on an empty input opens its command
         // palette, which a message cannot drive.
         _ => &[],