fix: invoke .sh hooks via bash prefix; add version for cache invalidation

Fixes #993 (Permission denied on hook scripts) without relying on
client-side +x preservation.

The hook executor spawns commands via /bin/sh -c, which requires +x
to execute a script directly. Prefixing with bash reads the script
as data — mode bits are irrelevant. This works on all Claude Code
versions, whereas the client-side chmod fix (claude-cli #24666) only
shipped in v2.1.86.

All 3 scripts declare #!/bin/bash and use bashisms ([[ ]], =~), so
bash (not sh) is the correct interpreter.

The version field forces a fresh cache path (1.0.0/ instead of
unknown/), ensuring the new hooks.json reaches users with stale
caches.

plugins/learning-output-style/.claude-plugin/plugin.json

@@ -1,5 +1,6 @@
 {
   "name": "learning-output-style",
+  "version": "1.0.0",
   "description": "Interactive learning mode that requests meaningful code contributions at decision points (mimics the unshipped Learning output style)",
   "author": {
     "name": "Anthropic",