v0.9.26 — BM ad-account dropdown shows every account

Fixed — mureo configure Meta ad-account dropdown now lists every account under a Business Manager (#181)

The configure UI's Meta ad-account picker silently truncated to the
first 25 accounts under any Business Manager because
list_meta_ad_accounts in mureo/meta_ads/accounts.py called
GET /me/adaccounts once and returned the first page verbatim.
Operators with mid-sized BM portfolios (26+ accounts) could not select
the account they actually wanted to connect — it never appeared in the
dropdown.

This release walks paging.next until exhausted (with limit=100 on
the first request to minimise round-trips) and concatenates every page
in cursor order. A 50-page hard cap stops a buggy Graph response from
spinning the configure UI forever; the cap path logs a warning so the
gap is visible to operators.

Two defence-in-depth additions land alongside the pagination fix:

• Host pinning on paging.next. Refuse to follow any URL whose
  host is not graph.facebook.com or whose scheme is not https.
  From page 2 onward the access token lives inside the cursor URL
  itself, so a tampered response (broken TLS pinning, proxy mis-route)
  could otherwise exfiltrate it.
• Token redaction in RuntimeError. Scrub the access token out
  of the wrapped exception message and break the exception chain with
  raise ... from None, so httpx.HTTPStatusError (whose __str__
  embeds the full request URL) cannot leak the token into operator
  logs or UI error surfaces on a mid-walk failure.

No public surface change — list_meta_ad_accounts(access_token) -> list[dict[str, Any]] is unchanged. Operators see the fix
immediately after upgrading to 0.9.26 the next time they run
mureo configure.