docs: scrub private-doc references from source comments (pre-publish)

Source comments pointed at gitignored docs/private/*.md design docs — harmless
(no secret) but dangling references in a public tree. Inlined the rationale and
dropped the pointers. Comment-only.

src/api/wallet/grin.rs

@@ -6,8 +6,7 @@
 //! wallet's outputs and read amounts, but cannot spend) and sends it per scan;
 //! the backend forwards it to grin-wallet's `scan_rewind_hash` and stores no
 //! secret. Spending (input selection, kernel signing) happens in the wallet; the
-//! backend only broadcasts the finalized transaction. See
-//! `docs/private/GRIN_LWS_DESIGN.md`.
+//! backend only broadcasts the finalized transaction.
 //!
 //! Conventions (matching [`super::btc_ltc`] / [`super::xmr_wow`]):
 //! * JWT-gated; the `rewind_hash` is a view credential — its request struct omits

src/api/wallet/grin_relay.rs

@@ -11,9 +11,8 @@
 //!
 //! Non-custodial by construction: the relay stores only opaque slatepack text
 //! (slatepacks are encrypted to the recipient's address) and lifecycle status. It
-//! never holds keys, never finalizes, never broadcasts — unlike the legacy
-//! backend, which finalized + broadcast server-side. See
-//! `docs/private/OWN_BACKEND_CONVERGENCE.md`.
+//! never holds keys, never finalizes, never broadcasts. The wallet finalizes and
+//! broadcasts locally; the relay is only a store-and-forward mailbox.
 //!
 //! Controls: JWT-gated; every action authorizes the caller as the slate's sender
 //! or recipient (a non-party gets 404, never an existence oracle); the recipient

src/infra/grin/mod.rs

@@ -7,7 +7,7 @@
 //! `scan_rewind_hash(rewind_hash, start_height)` does the chain scan (rangeproof
 //! rewind) and returns a [`ViewWallet`]; this client drives that, plus node
 //! status and broadcast. Spending (input selection, kernel signing) happens in
-//! the wallet, locally — never here. See `docs/private/GRIN_LWS_DESIGN.md`.
+//! the wallet, locally — never here.
 //!
 //! The Owner API v3 transport is an ECDH (secp256k1) handshake + AES-256-GCM
 //! channel; the secure session is initialized once (TOCTOU-free), the nonce