Injection panel UX: reachable auto re-attach + explain disabled controls

- The "Auto re-attach this game on relaunch" checkbox (and the Vulkan-layer
  checkbox) lived inside the connected-only block, so after a disconnect the
  control vanished while auto_reattach_ could stay enabled -- an active,
  invisible flag. Move both to render whenever a target is selected, connected or
  not, so they can be set up pre-launch and toggled off after disconnect.
- Explain why controls are greyed out: an inline hint under the subsystem toggles
  when no live game is connected, and a hover tooltip (AllowWhenDisabled) on the
  disabled "Inject & Connect" button telling the operator to pick a target.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -113,11 +113,6 @@ default** and covers anything the hooked path doesn't.
 From an in-depth review pass. Each item is fixed test-first (a failing test, then the fix) and lands
 as its own commit; "verify" items are confirmed real before any change, and dropped if not.
 
-UX:
-- **Auto re-attach control** — keep it visible/controllable when not connected (today it can be
-  enabled-but-invisible).
-- **Tooltips on disabled controls** — explain *why* Inject/subsystem controls are disabled.
-
 Code quality:
 - **Stale comments** — `hook_guard.hpp` top block (still the old destroy-on-remove model),
   `input_source.hpp` ("future" Steam source), `audio_ring.hpp` (v1/reserved), `shared_memory.hpp` /