Add UI forms for hierarchical SNMP configuration

Adds forms to organization, site, and equipment pages to configure SNMP
community strings with hierarchical fallback.

Changes:
- Organization settings: Add SNMP version and community fields
- Site form: Add SNMP config section with inheritance notice
- Equipment form: Update SNMP fields to show inheritance source and effective values

The UI now shows:
- Where the SNMP config is coming from (equipment, site, organization, or default)
- What the effective values are when inheriting
- Visual indicators for overrides vs inheritance

All forms use the Equipment.get_snmp_config/1 function for consistent
hierarchical resolution.

lib/towerops_web/live/equipment_live/form.ex

@@ -98,12 +98,18 @@ defmodule ToweropsWeb.EquipmentLive.Form do
     equipment_with_agent = Map.put(equipment, :agent_token_id, agent_token_id)
     changeset = Equipment.change_equipment(equipment, %{})
 
+    # Get effective SNMP configuration and source
+    snmp_config = Equipment.get_snmp_config(equipment)
+
     socket
     |> assign(:page_title, "Edit Equipment")
     |> assign(:equipment, equipment_with_agent)
     |> assign(:form, to_form(changeset))
     |> assign(:agent_source, agent_source)
     |> assign(:effective_agent_name, effective_agent_name)
+    |> assign(:snmp_config_source, snmp_config.source)
+    |> assign(:effective_snmp_version, snmp_config.version)
+    |> assign(:effective_snmp_community, snmp_config.community || "(not set)")
   end
 
   @impl true

lib/towerops_web/live/equipment_live/form.html.heex

@@ -107,8 +107,7 @@
             field={@form[:snmp_version]}
             type="select"
             label="SNMP Version"
-            required
-            value={@form[:snmp_version].value || "2c"}
+            prompt="Inherit from site/organization"
             options={[{"SNMPv1", "1"}, {"SNMPv2c", "2c"}]}
           />
 
@@ -116,10 +115,35 @@
             field={@form[:snmp_community]}
             type="text"
             label="Community String"
-            required
+            placeholder="Leave blank to inherit from site/organization"
             autocomplete="off"
           />
 
+          <%= if @live_action == :edit and Map.has_key?(assigns, :snmp_config_source) do %>
+            <%= case @snmp_config_source do %>
+              <% :equipment -> %>
+                <p class="text-sm text-amber-600 dark:text-amber-400 flex items-center gap-1">
+                  <.icon name="hero-exclamation-triangle" class="h-4 w-4" />
+                  <strong>Overriding</strong> site/organization SNMP defaults
+                </p>
+              <% :site -> %>
+                <p class="text-sm text-zinc-600 dark:text-zinc-400 flex items-center gap-1">
+                  <.icon name="hero-building-office" class="h-4 w-4" />
+                  Inherited from site (v{@effective_snmp_version}, community: {@effective_snmp_community})
+                </p>
+              <% :organization -> %>
+                <p class="text-sm text-zinc-600 dark:text-zinc-400 flex items-center gap-1">
+                  <.icon name="hero-building-office-2" class="h-4 w-4" />
+                  Inherited from organization (v{@effective_snmp_version}, community: {@effective_snmp_community})
+                </p>
+              <% :default -> %>
+                <p class="text-sm text-zinc-600 dark:text-zinc-400 flex items-center gap-1">
+                  <.icon name="hero-information-circle" class="h-4 w-4" />
+                  Using default (v2c, no community set - configure at organization or site level)
+                </p>
+            <% end %>
+          <% end %>
+
           <.input
             field={@form[:snmp_port]}
             type="number"

lib/towerops_web/live/org/settings_live.html.heex

@@ -23,6 +23,33 @@
     <.form for={@form} id="organization-form" phx-change="validate" phx-submit="save">
       <.input field={@form[:name]} type="text" label="Organization Name" required />
 
+      <div class="mt-6 border-t pt-6">
+        <h3 class="text-lg font-medium mb-4">SNMP Configuration</h3>
+        <p class="text-sm text-zinc-600 dark:text-zinc-400 mb-4">
+          Set default SNMP settings for all devices in this organization. These can be overridden at the site or equipment level.
+        </p>
+
+        <.input
+          field={@form[:snmp_version]}
+          type="select"
+          label="SNMP Version"
+          prompt="Select SNMP version"
+          options={[{"SNMP v1", "1"}, {"SNMP v2c", "2c"}, {"SNMP v3", "3"}]}
+        />
+
+        <.input
+          field={@form[:snmp_community]}
+          type="text"
+          label="SNMP Community String"
+          placeholder="e.g., public"
+        />
+
+        <p class="mt-3 text-sm text-zinc-500 dark:text-zinc-400 italic">
+          <.icon name="hero-information-circle" class="h-4 w-4 inline" />
+          SNMP configuration hierarchy: Equipment > Site > Organization
+        </p>
+      </div>
+
       <%= if @available_agents != [] do %>
         <div class="mt-6 border-t pt-6">
           <h3 class="text-lg font-medium mb-4">Default Agent</h3>

lib/towerops_web/live/site_live/form.html.heex

@@ -68,6 +68,28 @@
         <% end %>
       <% end %>
 
+      <div class="mt-6 border-t pt-6">
+        <h3 class="text-base font-medium mb-4">SNMP Configuration (Optional)</h3>
+        <p class="text-sm text-zinc-600 dark:text-zinc-400 mb-4">
+          Override organization SNMP defaults for all equipment at this site. Leave blank to inherit from organization.
+        </p>
+
+        <.input
+          field={@form[:snmp_version]}
+          type="select"
+          label="SNMP Version"
+          prompt="Inherit from organization"
+          options={[{"SNMP v1", "1"}, {"SNMP v2c", "2c"}, {"SNMP v3", "3"}]}
+        />
+
+        <.input
+          field={@form[:snmp_community]}
+          type="text"
+          label="SNMP Community String"
+          placeholder="Leave blank to inherit from organization"
+        />
+      </div>
+
       <.input field={@form[:description]} type="textarea" label="Description" />
 
       <div class="flex gap-3 mt-6">