fix(vault): backtick OAuth2 in new doc comments (clippy doc_markdown)

CI clippy flagged two unbackticked `OAuth2` doc items (the codebase
backticks it elsewhere). Verified with an isolated CARGO_TARGET_DIR
clippy run so the result doesn't share cargo's build cache (the source
of the repeated local false-greens).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: UnbreakableMJ

crates/vault-agent/src/state.rs

@@ -43,7 +43,7 @@ pub struct Vault {
     pub protected_user_key: String,
     /// Account KDF parameters (for offline master-key derivation / re-persist).
     pub kdf: vault_core::kdf::KdfParams,
-    /// OAuth2 refresh token (decrypted, in memory) when one is available — from
+    /// `OAuth2` refresh token (decrypted, in memory) when one is available — from
     /// the login token on an online unlock, or decrypted from the cache on an
     /// offline/PIN unlock. Lets a token-less session go online via
     /// [`Vault::ensure_online`] and is persisted (encrypted) by `persist_cache`.

crates/vault-store/src/lib.rs

@@ -63,7 +63,7 @@ pub struct VaultCache {
     /// agent restart; reset to 0 on a correct PIN or a fresh enrollment.
     #[serde(default)]
     pub pin_failures: u32,
-    /// The OAuth2 refresh token encrypted under the user key (an `EncString`),
+    /// The `OAuth2` refresh token encrypted under the user key (an `EncString`),
     /// so a cache/PIN unlock can mint a live access token without the master
     /// password. `None` when none has been persisted.
     #[serde(default)]