docs: add Python quickstart for Stellar stealth payments (#143)

* docs: add Python quickstart for Stellar stealth payments

Covers the full flow for Python 3.11+ backends that want to talk to
Wraith contracts without the TypeScript SDK:

- guides/quickstarts/python.mdx (new)
  - pip install stellar-sdk + cryptography only
  - wraith_crypto.py inline utility: scan-key derivation via SHA-256
    domain separation, X25519 ECDH, ed25519 point addition, view-tag
    prefilter, sign_with_scalar (RFC 8032 compatible raw scalar signing)
  - Fetch WRAITH_ANNOUNCEMENT events from Soroban RPC (getEvents + XDR decode)
  - scan_announcements with view-tag prefilter (~255/256 skip rate)
  - Send: createAccount activation + Soroban announcer invocation
  - Spend: withdrawal tx signed with raw stealth scalar
  - All Python fences marked no-check for the TS snippet gate
  - Targets futurenet; notes testnet contract IDs for live testing

- sdk/overview.mdx: cross-link to Python quickstart under Next Steps

- docs.json: Quickstarts nav group added above Guides in the Guides tab

* fix(docs): merge duplicate pages key in Quickstarts nav group

---------

Co-authored-by: musay <ochoalaurie@gmail.com>

Author: Mathew2k-hash

docs.json

@@ -124,7 +124,10 @@
         "groups": [
           {
             "group": "Quickstarts",
-            "pages": ["guides/quickstarts/rust"]
+            "pages": [
+              "guides/quickstarts/python",
+              "guides/quickstarts/rust"
+            ]
           },
           {
             "group": "Guides",