feat: add fluxer upstream source and self-hosting documentation

- Clone of github.com/fluxerapp/fluxer (official upstream)
- SELF_HOSTING.md: full VM rebuild procedure, architecture overview,
  service reference, step-by-step setup, troubleshooting, seattle reference
- dev/.env.example: all env vars with secrets redacted and generation instructions
- dev/livekit.yaml: LiveKit config template with placeholder keys
- fluxer-seattle/: existing seattle deployment setup scripts

fluxer/fluxer_gateway/src/gateway/gateway_rpc_misc.erl

@@ -0,0 +1,68 @@
+%% Copyright (C) 2026 Fluxer Contributors
+%%
+%% This file is part of Fluxer.
+%%
+%% Fluxer is free software: you can redistribute it and/or modify
+%% it under the terms of the GNU Affero General Public License as published by
+%% the Free Software Foundation, either version 3 of the License, or
+%% (at your option) any later version.
+%%
+%% Fluxer is distributed in the hope that it will be useful,
+%% but WITHOUT ANY WARRANTY; without even the implied warranty of
+%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+%% GNU Affero General Public License for more details.
+%%
+%% You should have received a copy of the GNU Affero General Public License
+%% along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+
+-module(gateway_rpc_misc).
+
+-export([execute_method/2, get_local_node_stats/0]).
+
+-spec execute_method(binary(), map()) -> map().
+execute_method(<<"process.memory_stats">>, Params) ->
+    Limit =
+        case maps:get(<<"limit">>, Params, undefined) of
+            undefined ->
+                100;
+            LimitValue ->
+                validation:snowflake_or_throw(<<"limit">>, LimitValue)
+        end,
+    Guilds = process_memory_stats:get_guild_memory_stats(Limit),
+    GuildsWithStringMemory = [G#{memory := integer_to_binary(maps:get(memory, G))} || G <- Guilds],
+    #{<<"guilds">> => GuildsWithStringMemory};
+execute_method(<<"process.node_stats">>, _Params) ->
+    get_local_node_stats().
+
+-spec get_local_node_stats() -> map().
+get_local_node_stats() ->
+    SessionCount = get_manager_count(session_manager),
+    GuildCount = get_manager_count(guild_manager),
+    PresenceCount = get_manager_count(presence_manager),
+    CallCount = get_manager_count(call_manager),
+    MemoryInfo = erlang:memory(),
+    TotalMemory = proplists:get_value(total, MemoryInfo, 0),
+    ProcessMemory = proplists:get_value(processes, MemoryInfo, 0),
+    SystemMemory = proplists:get_value(system, MemoryInfo, 0),
+    #{
+        <<"status">> => <<"healthy">>,
+        <<"sessions">> => SessionCount,
+        <<"guilds">> => GuildCount,
+        <<"presences">> => PresenceCount,
+        <<"calls">> => CallCount,
+        <<"memory">> => #{
+            <<"total">> => integer_to_binary(TotalMemory),
+            <<"processes">> => integer_to_binary(ProcessMemory),
+            <<"system">> => integer_to_binary(SystemMemory)
+        },
+        <<"process_count">> => erlang:system_info(process_count),
+        <<"process_limit">> => erlang:system_info(process_limit),
+        <<"uptime_seconds">> => element(1, erlang:statistics(wall_clock)) div 1000
+    }.
+
+-spec get_manager_count(atom()) -> non_neg_integer().
+get_manager_count(Manager) ->
+    case gen_server:call(Manager, get_global_count, 1000) of
+        {ok, Count} -> Count;
+        _ -> 0
+    end.