Refactor addon system: derive module list from build.zig, prune inactive prefixes at runtime

- Eliminate hardcoded module_names in addons.zig — now derived from
  build.zig via all_module_names build option
- Add module_active.zig runtime registry: main.zig registers isActive
  pointers during install(), addons.zig queries them without importing
  each module directly
- Prune embedded file prefixes at startup: after all modules claim
  mutexes, build a runtime active_prefixes table excluding modules we
  don't own. findEmbeddedFile searches only active entries — no
  per-lookup isActive check on the hot path
- Tag both addon and asset prefixes with module_name so pruning applies
  to all embedded files for a module
- Rename src/markers/ → src/worldmarkers/, src/outline/api.zig →
  src/outline/outline.zig to follow {name}/{name}.zig convention

src/module_active.zig

@@ -0,0 +1,26 @@
+// Runtime registry for module isActive() function pointers.
+// Populated by main.zig during install(), queried by addons.zig during login.
+// Exists solely to avoid duplicating module imports in addons.zig.
+
+const std = @import("std");
+
+const MAX = 32;
+var names: [MAX][*:0]const u8 = undefined;
+var fns: [MAX]*const fn () bool = undefined;
+var count: usize = 0;
+
+/// Register a module's isActive function. Called from main.zig install().
+pub fn register(name: [*:0]const u8, f: *const fn () bool) void {
+    if (count >= MAX) return;
+    names[count] = name;
+    fns[count] = f;
+    count += 1;
+}
+
+/// Check if a module is active by name. Returns true if unknown (no isActive).
+pub fn isActive(name: [*:0]const u8) bool {
+    for (0..count) |i| {
+        if (std.mem.orderZ(u8, names[i], name) == .eq) return fns[i]();
+    }
+    return true;
+}