* docs: correct MODULE_NOT_FOUND plugin cache path
Point the install command at cache/ecc/ecc/<version>.
The cache/ecc directory itself has no package.json.
* docs: explain the MODULE_NOT_FOUND version placeholder
Tell readers to replace <version> with the version from claude plugin list
before running the install command.
* docs: quote plugin cache version placeholder
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Co-authored-by: haelyra <49814733+haelyra@users.noreply.github.com>