feat(sched): global task registry to be able to enumerate system-wide processes + stellux proc kill system call

[FlareCoding]

Note

High Risk
Touches core scheduler/task lifecycle by inserting/removing tasks from a new global registry during creation and reaping, which could introduce race conditions or leaks if ordering is wrong. Also adds a new process-control syscall (proc_kill_tid) that can terminate tasks system-wide, so correctness and permission checks are security/stability relevant.

Overview
Introduces a global sched::g_task_registry (hashmap keyed by TID) to track all tasks and support system-wide enumeration via snapshotting.

Scheduler/task teardown paths now register tasks on creation and unregister them on cleanup (including the unstarted-task destroy path), and the scheduler init now initializes the registry.

Adds a new syscall SYS_PROC_KILL_TID / proc_kill_tid that looks up a task by TID via the registry and forces a kill-wake for userland tasks, rejecting idle/kernel/self targets with appropriate errors; userland gains a proc_kill_tid() wrapper and a new kill app.

Fixes a poll/wake race by resolving aborted poll_wait blocking so the task doesn’t continue running with a queued sched_link, and adds debug-only detection for ready-list double-enqueue; includes extensive new unit/integration tests covering the registry and the poll race.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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No authorization check in proc_kill_tid syscall

Medium Severity · Security Issue

The proc_kill_tid syscall allows any userland process to kill any other userland process by TID with no ownership or permission check. The existing proc_kill uses handle-based authorization (callers can only kill processes they created), but proc_kill_tid bypasses this entirely — only checking that the target isn't a kernel or idle task. Any unprivileged process knowing a TID can terminate an arbitrary user process.