feat: provider-strict configs, slot-based templates, broadcast targets, email bots, command templates

Major architectural improvements:
- Provider-type enforcement: configs validated against provider type at assignment
- TemplateConfig migrated to slot-based pattern (TemplateSlot child table)
- Broadcast targets: TargetReceiver child table for multi-receiver dispatch
- EmailBot: first-class email sender entity with SMTP config, test connection
- CommandTemplateConfig: generic slot-based command response templates
- Provider capability registry: dynamic slot/event/command definitions per provider
- CommandTracker play/pause button matches NotificationTracker style

packages/server/src/notify_bridge_server/commands/handler.py

@@ -17,6 +17,8 @@ from ..database.engine import get_engine
 from ..services import make_immich_provider
 from ..database.models import (
     CommandConfig,
+    CommandTemplateConfig,
+    CommandTemplateSlot,
     CommandTracker,
     CommandTrackerListener,
     EventLog,
@@ -51,6 +53,23 @@ def _check_rate_limit(bot_id: int, chat_id: str, cmd: str, limits: dict[str, int
     return None
 
 
+def _render_cmd_template(
+    templates: dict[str, str], slot_name: str, context: dict[str, Any]
+) -> str | None:
+    """Try to render a command template. Returns None if no template or error."""
+    template_str = templates.get(slot_name)
+    if not template_str:
+        return None
+    try:
+        from jinja2.sandbox import SandboxedEnvironment
+        env = SandboxedEnvironment(autoescape=False)
+        tmpl = env.from_string(template_str)
+        return tmpl.render(**context)
+    except Exception as e:
+        _LOGGER.warning("Failed to render command template '%s': %s", slot_name, e)
+        return None
+
+
 async def _resolve_command_context(
     bot: TelegramBot,
 ) -> list[tuple[CommandTracker, CommandConfig, ServiceProvider]]:
@@ -87,7 +106,20 @@ async def _resolve_command_context(
                 continue
             tuples.append((tracker, config, provider))
 
-        return tuples
+        # Load command template slots from the first config that has one
+        cmd_template_slots: dict[str, str] = {}
+        for _, config, _ in tuples:
+            if config.command_template_config_id:
+                slot_result = await session.exec(
+                    select(CommandTemplateSlot).where(
+                        CommandTemplateSlot.config_id == config.command_template_config_id
+                    )
+                )
+                cmd_template_slots = {s.slot_name: s.template for s in slot_result.all()}
+                if cmd_template_slots:
+                    break
+
+        return tuples, cmd_template_slots
 
 
 def _merge_command_context(
@@ -125,10 +157,13 @@ async def handle_command(
     if not cmd:
         return None
 
-    ctx = await _resolve_command_context(bot)
-    enabled, locale, response_mode, default_count, rate_limits = _merge_command_context(ctx)
+    ctx_tuples, cmd_templates = await _resolve_command_context(bot)
+    enabled, locale, response_mode, default_count, rate_limits = _merge_command_context(ctx_tuples)
 
     if cmd == "start":
+        result = _render_cmd_template(cmd_templates, "start", {"locale": locale, "bot_name": bot.name})
+        if result:
+            return result
         msgs = {
             "en": "Hi! I'm your Notify Bridge bot. Use /help to see available commands.",
             "ru": "Привет! Я бот Notify Bridge. Используйте /help для списка команд.",
@@ -141,6 +176,9 @@ async def handle_command(
     # Rate limit check
     wait = _check_rate_limit(bot.id, chat_id, cmd, rate_limits)
     if wait is not None:
+        result = _render_cmd_template(cmd_templates, "rate_limited", {"wait": wait, "locale": locale})
+        if result:
+            return result
         msgs = {
             "en": f"Please wait {wait}s before using this command again.",
             "ru": f"Подождите {wait} сек. перед повторным использованием.",
@@ -151,7 +189,7 @@ async def handle_command(
 
     # Build providers map from command context
     providers_map: dict[int, ServiceProvider] = {}
-    for _, _, provider in ctx:
+    for _, _, provider in ctx_tuples:
         providers_map[provider.id] = provider
 
     # Dispatch