[Bug]: Broken clone URL in always-on-memory-agent README (still unfixed after #2664)

### File Name

gemini/agents/always-on-memory-agent/README.md

### What happened?

## What happened

The Quick Start in `gemini/agents/always-on-memory-agent/README.md` tells users to clone a repo that no longer exists:

git clone https://github.com/Shubhamsaboo/always-on-memory-agent.git
cd always-on-memory-agent

`Shubhamsaboo/always-on-memory-agent` returns 404, so this step fails immediately and blocks anyone trying to run the sample.

## How to reproduce

Follow step 1 of the README's Quick Start and run the `git clone` command above.

## Expected

The repo clones and you can `cd` into the sample.

## Actual

`fatal: repository not found` - the target repo is gone.

## Prior attempt

PR #2664 proposed this same fix in March but was closed un-merged; the only blocker was an unsigned CLA, not any objection to the change. The bug is still present in `main`.

## Suggested fix

Since the sample lives in this monorepo, replace the Install block with a sparse-checkout of its subdirectory:

git clone --depth 1 --filter=blob:none --sparse \
https://github.com/GoogleCloudPlatform/generative-ai.git
cd generative-ai
git sparse-checkout set gemini/agents/always-on-memory-agent
cd gemini/agents/always-on-memory-agent
pip install -r requirements.txt

Verified these commands check out the sample cleanly. No code changes; the Project Structure tree stays valid since the working directory is still `always-on-memory-agent/`.

I have the fix on a branch but can't open a PR (repo restricts PR creation to collaborators). It's here as a cross-fork compare, ready for a maintainer to open as a PR or apply directly:

https://github.com/GoogleCloudPlatform/generative-ai/compare/main...yrangana:generative-ai:patch-1

### Relevant log output

```shell
fatal: repository 'https://github.com/Shubhamsaboo/always-on-memory-agent.git/' not found
```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Open gemini/agents/always-on-memory-agent/README.md and inspect the Quick Start Install block, then run the current clone command to reproduce the 404. Use the supplied sparse-checkout commands as the reference, and verify that they check out the sample and reach its directory before installing requirements.txt.

Written by the indexing model from the issue text.