Throw out_of_range.411 instead of asserting on JSON Patch "add" to a primitive parent

[nlohmann]

Summary

A JSON Patch add whose target location has a parent that is neither an object nor an array (e.g. add /xyz/1/lmn where /xyz/1 is a string) previously hit an internal JSON_ASSERT(false) in patch_inplace. This meant:

• debug builds aborted the process (SIGABRT), and
• release builds (NDEBUG) silently dropped the operation, returning a wrong result with no error.

Per RFC 6902, such a target is invalid because its parent cannot receive a new member or element. This is now reported with a proper, catchable exception.

Fixes #4292.

Changes

• Replace the unreachable-assertion branch in operation_add with a new exception code out_of_range.411: "cannot add value: the JSON Patch 'add' target's parent is of type , but must be an object or array" (include/ and single_include/).
• Document out_of_range.411 in exceptions.md, and add Exceptions + Version history entries to patch.md / patch_inplace.md.
• Add regression tests in unit-json_patch.cpp (string/number parent, plus the original two-step sequence from the issue) and a positions-aware exact-message test in unit-diagnostic-positions.cpp.

Notes

• A new public exception id (out_of_range.411) is introduced; behavior for previously-valid patches is unchanged.
• Verified green with JSON_Diagnostics OFF and ON; the debug-abort and the release silent-no-op are both eliminated.