docs(web-client): Add Private Note Transfer tutorial with Note Transport Service and fetchPrivate()

### Problem / Context
Under `docs/src/web-client/`, there are runnable web tutorials for public note operations (`mint_consume_create_tutorial.md`), counter contracts, and foreign procedure invocations, but **no tutorial for Private Note transfers**.

In addition, existing notes in `mint_consume_create_tutorial.md` state that private notes must be exchanged manually out-of-band. Now that `@miden-sdk/miden-sdk` natively supports `client.notes.sendPrivateNote()` and `client.notes.fetchPrivate()` via the Note Transport Service, web dApp developers need a dedicated, end-to-end tutorial.

### Proposed Solution
Add a new step-by-step tutorial at `docs/src/web-client/private_notes_tutorial.md` demonstrating:
1. Initializing `MidenClient` from `@miden-sdk/miden-sdk` in a Vite/React web app.
2. Creating and sending a private P2ID note using `client.notes.sendPrivateNote()`.
3. Transporting note metadata and fetching recipient private notes via `client.notes.fetchPrivate()`.
4. Consuming the private note on the recipient web client and asserting updated account vault balances.
5. Updating outdated private note disclaimers in `mint_consume_create_tutorial.md` to link to this new tutorial.

### Expected Impact
Fills the missing web tutorial gap and provides frontend developers with a runnable TypeScript reference for Miden's flagship privacy feature.

I would like to write and submit this tutorial. Could a maintainer please assign this issue to me?

The tutorial will be created in docs/src/web-client/private_notes_tutorial.md. Start by reviewing the existing mint_consume_create_tutorial.md to understand the format and the MidenClient setup. The new tutorial must demonstrate sendPrivateNote() and fetchPrivate() using the @miden-sdk/miden-sdk. Update the old tutorial's disclaimers to link to the new one. Verify the steps work in a Vite/React environment.

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