goblin: mark deferred audit items (M5, M6, L2, L3, L4) with TODO tags

Comments only, no behavior change: tag the five deferred audit findings at the
code they refer to so they are findable later. M5 (widen display escaping to
category-based) and M6 (template echo vs re-serialization) in authuri; L2
(redact secrets from Debug) at NostrIdentity; L3 (carry secrets as ZeroingString
end-to-end) at get_nostr_nsec; L4 (reset AdvancedState on back) in the goblin
on_back handler.

src/gui/views/goblin/mod.rs

@@ -664,6 +664,8 @@ impl GoblinWalletView {
 			if self.settings_page == SettingsPage::Identities {
 				self.identity_switch = IdentitySwitchState::default();
 			}
+			// TODO(audit L4): reset AdvancedState on back navigation too, so a
+			// revealed nsec/password does not survive leaving the Advanced page.
 			self.settings_page = SettingsPage::Main;
 			return false;
 		}

src/nostr/authuri.rs

@@ -300,6 +300,8 @@ pub(crate) fn domain_bound(callback: &str, domain: &str) -> bool {
 /// arrays of strings. A `delegation` tag is rejected outright (defense in depth,
 /// even though delegation tokens are unreachable here). Any deviation rejects.
 fn validate_template(raw: &str) -> Option<Template> {
+	// TODO(audit M6): consider byte-exact template echo vs structural
+	// re-serialization; needs magick server co-design.
 	// Percent-decode for parity with the other params (base64url never needs
 	// encoding, so this is a no-op on well-formed input), then enforce the
 	// strict unpadded-base64url charset ourselves.
@@ -478,6 +480,8 @@ pub fn content_preview(content: &str) -> (String, usize) {
 /// passes through unchanged. Used on ALL requester-controlled strings (content,
 /// tag values, titles) before they reach a label.
 pub fn escape_for_display(s: &str) -> String {
+	// TODO(audit M5): widen escaping to category-based (all C0/C1, bidi controls)
+	// rather than the current explicit list.
 	let mut out = String::with_capacity(s.len());
 	for c in s.chars() {
 		let code = c as u32;

src/nostr/identity.rs

@@ -38,6 +38,7 @@ pub enum IdentitySource {
 }
 
 /// Identity file stored at `wallet_data/nostr/identity.json`.
+// TODO(audit L2): redact secret material (the ncryptsec) from Debug output.
 #[derive(Serialize, Deserialize, Clone, Debug)]
 pub struct NostrIdentity {
 	pub ver: u8,

src/wallet/wallet.rs

@@ -588,6 +588,8 @@ impl Wallet {
 	/// wrong password can never leak the key. The value is derived on demand and
 	/// never persisted.
 	pub fn get_nostr_nsec(&self, password: String) -> Result<String, String> {
+		// TODO(audit L3): carry secrets (the password and the returned nsec) as
+		// ZeroingString end-to-end rather than plain String.
 		let svc = self
 			.nostr_service()
 			.ok_or_else(|| "nostr identity not ready".to_string())?;