Remove deprecated classes and static singleton-based architecture

docs/threading.md

@@ -0,0 +1,45 @@
+# Threading & Scheduling
+
+**Package:** `me.bobert.netneutrality.platform.concurrency`
+
+This subsystem centralizes asynchronous execution and recurring jobs.
+
+## Classes
+
+| Class | Responsibility |
+|---|---|
+| `ThreadManager` | Static registry of `ExecutorService` instances shared across the bot. |
+| `BaseThreadFactory` | Custom `ThreadFactory` giving threads meaningful names and an uncaught-exception handler. |
+| `ScheduledTaskManager` | Schedules and cancels recurring [scheduled tasks](tasks.md#34-scheduled-tasks). |
+
+## `ThreadManager`
+
+- `getScheduledExecutor()` — a `ScheduledThreadPool` sized to the number of CPU cores.
+- `getExecutor(name)` — returns (and caches) a named thread pool for ad-hoc async work.
+- `shutdownExecutor()` — shuts the executors down cleanly; called from
+  [`App.shutdown()`](architecture.md#shutdown-lifecycle).
+
+## `BaseThreadFactory`
+
+Names created threads (e.g. `web-api-1`) so they are identifiable in logs and stack dumps, and installs
+an [`ExecutorException`](utilities-and-bootstrap.md#exceptions) as the thread's
+`UncaughtExceptionHandler` so crashes on worker threads are still routed through
+[`LogHandler`](utilities-and-bootstrap.md#loghandler). It is used both by `ThreadManager` and by the
+[Web API](web-api.md) server pool.
+
+## `ScheduledTaskManager`
+
+Coordinates [`ScheduledTask`](tasks.md#34-scheduled-tasks) instances (discovered reflectively at
+startup by [`TaskManager.init()`](tasks.md#taskmanager)):
+
+- `schedule(ScheduledTask task)` — schedules the task at a fixed delay/interval derived from its
+  `TimeFrame` (minutely / hourly / daily / custom), using the shared scheduled executor.
+- `cancelAll()` — cancels every scheduled task; called first in
+  [`App.shutdown()`](architecture.md#shutdown-lifecycle).
+
+The existing scheduled tasks are `MusicManagerCleanup`, `MusicPlayerAutoDisconnect`, and
+`TaskCleanup` (see the [task catalog](tasks.md#concrete-task-catalog)).
+
+> **Direction of travel:** the scheduled-task abstraction is intended to eventually replace ad-hoc
+> threads created via `ThreadManager`, giving a single, uniform way to express recurring background
+> work. It is still evolving (see [tasks.md §3.4](tasks.md#34-scheduled-tasks)).