Add shell completion generation

docs/roadmap.md

@@ -65,6 +65,10 @@ Implementation order:
    - `[x]` README has a two-machine walkthrough for the main smoke tests.
    - `[x]` CLI recovery errors tell operators the next command to run.
    - `[x]` JSON sync status is script-friendly for stale/failed peer detection.
+   - `[x]` Shell completions are generated from the Clap command tree for
+     bash, zsh, fish, PowerShell, and elvish.
+   - `[x]` Completion installation examples are available through
+     `geth guide completions`.
 
 - `[x]` Two-node operator-flow test coverage.
   Acceptance criteria: