fix(install): normalize null hook matcher → "" on merge (Claude Code /doctor)

Users with pre-kit hooks that have no `matcher` field end up with matcher:null,
which Claude Code /doctor rejects ("Expected string, but received null") and
skips the whole settings file. The jq merge preserved null as-is, so every
reinstall re-surfaced the error. Now map(.matcher //= "") before group_by →
null/absent collapses to "" (match-all), one group per matcher.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

install/lib-hooks.sh

@@ -60,6 +60,10 @@ _jq_merge_hooks() {
     | reduce ($add.hooks | keys[]) as $phase ($orig;
         .hooks[$phase] = (
           ((.hooks[$phase] // []) + ($add.hooks[$phase] // []))
+          # Normalize null/absent matcher → "" (Claude Code /doctor rejects null;
+          # user's pre-kit hooks often have no matcher field). Before group_by so
+          # null + "" collapse into one group.
+          | map(.matcher //= "")
           | group_by(.matcher)
           | map(
               .[0].matcher as $m