chore(cli): bump to v0.2.6 + revert unrelated __init__.py docstring

Addresses review feedback on #5152:

  - Revert the mem0/__init__.py module docstring (was a misguided
    workaround to fire ci.yml; reviewer correctly flagged as unrelated)
  - Bump cli-python and cli-node to 0.2.6 so the claim-flow tip wording
    fix ships to users in the next release
  - Add CLI v0.2.6 changelog entry under docs/changelog/sdk.mdx

The build_mem0/build_embedchain required-check stalemate on docs-only
PRs needs a proper ci.yml fix in a separate PR (passthrough job for
the path-filter-skipped case). Admin override needed for this PR.

cli/node/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@mem0/cli",
-  "version": "0.2.5",
+  "version": "0.2.6",
   "description": "The official CLI for mem0 — the memory layer for AI agents",
   "type": "module",
   "bin": {