fix: model abbreviation without settings.json, add agent install prompt

The else branch (no configured_model) used the generic family name
"opus" instead of abbreviating model_id. On CI and fresh installs
where ~/.claude/settings.json has no model override, "claude-opus-4-6[1m]"
displayed as "opus[1m]" instead of "opus4.6[1m]". Now tries
abbreviate_model_id on model_id before falling back to family name.

Also add a one-shot Claude Code prompt to README for agent-assisted install.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: lroolle

README.md

@@ -28,6 +28,14 @@ Restart Claude Code (or send a message) and the statusline appears.
 
 **Requires:** Bash, `jq`, `curl`.
 
+### Install via Claude Code
+
+Paste this into Claude Code and it will set everything up:
+
+```
+Install claude-code-statusline: download https://raw.githubusercontent.com/thevibeworks/claude-code-statusline/main/statusline.sh to ~/.claude/statusline.sh, make it executable, and add a statusLine command entry to ~/.claude/settings.json pointing to it with padding 0.
+```
+
 <details><summary>Manual install / inspect first</summary>
 
 ```bash

statusline.sh

@@ -1211,7 +1211,13 @@ if [ -n "$configured_model" ]; then
         model_text="${model_text}[1m]"
     fi
 else
-    model_text="$runtime_model"
+    base_id="${model_id%%\[*\]}"
+    abbreviated=$(abbreviate_model_id "$base_id")
+    if [ "$abbreviated" != "$base_id" ]; then
+        model_text="$abbreviated"
+    else
+        model_text="$runtime_model"
+    fi
     if is_1m_model; then
         model_text="${model_text}[1m]"
     fi