modules: capability-scoped Store/NetView boundary (Tier 2)

Services no longer receive the concrete account store. on_command now takes
&mut dyn Store + &dyn NetView (both defined in fedserv-api); the engine's Db
and Network implement them. Reads hand back plain views (AccountView,
ChannelView, ...) carrying only non-secret fields, so the event log, gossip,
and credential material (password hash, SCRAM verifiers) are unreachable from
a module. All command modules ported; behaviour unchanged.

modules/nickserv/resetpass.rs

@@ -1,9 +1,9 @@
-use crate::engine::db::{CodeKind, Db};
+use crate::engine::db::{CodeKind, Store};
 use crate::engine::service::{Sender, ServiceCtx};
 
 // RESETPASS <account>: email a reset code to the address on file.
 // RESETPASS <account> <code> <newpassword>: complete the reset with that code.
-pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db: &mut Db) {
+pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db: &mut dyn Store) {
     if !db.email_enabled() {
         ctx.notice(me, from.uid, "Password reset by email isn't available here.");
         return;