Add friends, markers, HUD overlays, tab complete

- FriendsManager persists a per-user friend list at config/clientirc-friends.json.
- MarkerManager holds one ephemeral marker per owner (5 min expiry).
- IRC protocol extended with marker_set / marker_remove; server relays them.
- IrcService DisplayLine replaced with sealed IrcEvent (Chat / System / MarkerSet / MarkerRemove); chat formatting moved into the client.
- ClientIrcMod handles .friends add/remove/list, .marker remove, .help; chat lines from friends are prefixed with a green dot; marker events from non-friends are ignored.
- OverlayHud draws a top-center compass strip and a top-left watermark (nick / FPS / ping) via HudLayerRegistrationCallback.
- WorldOverlayRenderer draws green crosses above friends and magenta beams + base cubes at active markers via WorldRenderEvents.AFTER_ENTITIES.
- MiddleClickHandler binds MMB via KeyMapping, raycasts a block or 20-block look ray, stores locally and sends marker_set on a daemon executor.
- ChatScreenMixin completes . prefix commands on Tab; first mixin in the project, plumbed through clientirc.client.mixins.json and fabric.mod.json.

src/client/java/ru/nevetime/clientirc/mixin/ChatScreenMixin.java

@@ -0,0 +1,49 @@
+package ru.nevetime.clientirc.mixin;
+
+import net.minecraft.client.gui.components.EditBox;
+import net.minecraft.client.gui.screens.ChatScreen;
+import org.lwjgl.glfw.GLFW;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Mixin(ChatScreen.class)
+public abstract class ChatScreenMixin {
+    @Shadow protected EditBox input;
+
+    private static final String[] CLIENTIRC_COMMANDS = new String[] {
+        ".irc",
+        ".irc status",
+        ".irc reconnect",
+        ".irc reload",
+        ".friends add ",
+        ".friends remove ",
+        ".friends list",
+        ".marker remove",
+        ".help"
+    };
+
+    @Inject(method = "keyPressed", at = @At("HEAD"), cancellable = true)
+    private void clientirc$tabComplete(int keyCode, int scanCode, int modifiers, CallbackInfoReturnable<Boolean> cir) {
+        if (keyCode != GLFW.GLFW_KEY_TAB) return;
+        if (input == null) return;
+        String value = input.getValue();
+        if (value == null || !value.startsWith(".")) return;
+
+        String best = null;
+        for (String candidate : CLIENTIRC_COMMANDS) {
+            if (candidate.startsWith(value) && !candidate.equals(value)) {
+                if (best == null || candidate.length() < best.length()) {
+                    best = candidate;
+                }
+            }
+        }
+        if (best != null) {
+            input.setValue(best);
+            input.setCursorPosition(best.length());
+            cir.setReturnValue(true);
+        }
+    }
+}