refactor: drop dead scheduler raw_value deferral, route url messages to worker

The raw_value/computed_value handoff on WebSchedulerService is no longer
used now that command_message()/command_sendmail() compute synchronously,
so remove the members and the dead block in the scheduler loop.

Also drop the system/message special-case in dispatchCommand(): a
system/message whose value embeds a {url} now blocks at execution time
like any other internal command, so it should be offloaded to the
command worker task (large stack, off the main loop) instead of running
inline. Update the now-stale comments.

Co-authored-by: Proddy <proddy@users.noreply.github.com>

src/web/WebCommandService.cpp

@@ -141,9 +141,8 @@ bool WebCommandService::dispatchCommand(const char * name, const char * value) {
             if (isUrlCommand(ci->cmd.c_str())) {
                 return queueCommand(name, value);
             }
-            // system/message defers evaluation of its value (via the scheduler's raw_value),
+            // internal command whose value embeds a {url} fetch (e.g. system/message) - the value is
-            // so executing it never blocks - keep it synchronous even if the value has a {url}
+            // resolved by compute() at execution time and would block, so offload it to the worker task
-            if (Helpers::toLower(ci->cmd.c_str()) != "system/message") {
             // the effective value is the override if given, else the command's stored default
             const std::string effective_value = value ? value : std::string(ci->value.c_str());
             if (valueContainsUrl(effective_value)) {
@@ -151,7 +150,6 @@ bool WebCommandService::dispatchCommand(const char * name, const char * value) {
             }
         }
     }
-    }
 #endif
     return executeCommand(name, value);
 }
@@ -240,8 +238,8 @@ bool WebCommandService::executeCommand(const char * name, const std::string & co
     // run the value through the shunting-yard calculator so expressions like "custom/heatcnt + 1"
     // are resolved (entity references replaced by their values, then computed). Plain values pass
     // through unchanged. Applies to both URL and internal commands, like the old scheduler code
-    // which computed the value before executing. system/message evaluates its own argument later
+    // which computed the value before executing. system/message runs the shunting-yard on its own
-    // (deferred via the scheduler's raw_value), so pre-computing it would run it twice - pass raw.
+    // argument, so pre-computing it here would run it twice - pass it through raw.
     std::string computed_data = data;
     if (!data.empty() && cmd != "system/message") {
         computed_data = compute(data);

src/web/WebSchedulerService.cpp

@@ -367,11 +367,6 @@ void WebSchedulerService::loop() {
     static uint32_t last_uptime_min = 0;
     static uint32_t last_uptime_sec = 0;
 
-    if (!raw_value.empty()) {
-        computed_value = compute(raw_value);
-        raw_value.clear();
-    }
-
     if (scheduleItems_->empty()) {
         return;
     }

src/web/WebSchedulerService.h

@@ -75,9 +75,6 @@ class WebSchedulerService : public StatefulService<WebScheduler> {
 
     std::string get_metrics_prometheus();
 
-    std::string raw_value;
-    std::string computed_value;
-
 #if defined(EMSESP_TEST)
     void load_test_data();
 #endif