Add hyprctl command cwd to / - #14

…treamController#16, StreamController#127)

- Page.set_media_fps live-applied to matching inputs on ALL controllers:
  editing one page's FPS row rebased the playing video timeline on another
  deck showing a different page (self-corrects only on that deck's next
  page load). Now filtered by active page, the same filter update_input
  uses (issue StreamController#14).

- mark_page_ready_to_clear dereferenced active_page at call time; both
  bracketing callers (the tick loop and the key handler) re-derefed it for
  the True-call, so a page switch during a slow on_tick left the OLD page
  pinned ready_to_clear=False forever -- unevictable, silently shrinking
  the eviction budget. The False-call now returns the page it marked and
  the True-calls pass it back (issue StreamController#16).

- Page.initialize_actions' bare check-then-set on on_ready_called let two
  concurrent load_page(samePage) calls both claim the same action and
  submit a second concurrent on_ready (duplicate backend processes -- the
  class StreamController#34 closed for the on_update path). The claim is now atomic under
  a per-page lock; the loads and pool submit stay outside it (issue StreamController#127).

tests/scenario_small_guards.py red-checks all three: the FPS bleed, the
pinned page, and (via a capture-before-rendezvous barrier property making
the interleave deterministic) the double claim.

…overage

Review round 1 follow-ups to !41 (StreamController#14/StreamController#16/StreamController#127), test-only:

- StreamController#16 end-to-end: check_ready_to_clear_evicts_end_to_end drives the mid-work
  tick bracket, then runs the REAL clear_old_cached_pages and asserts the page
  is actually EVICTED -- the previous check only asserted the flag value, not
  that the fix restores evictability (the point of the bug). Red-tested:
  pre-fix the page stays pinned ready_to_clear=False and survives eviction.

- StreamController#16 key-handler: check_ready_to_clear_key_handler drives the real
  ControllerKey.event_callback (3706/3737) with a press-triggered page change
  injected at self.update() -- lands the switch mid-bracket. Asserts the OLD
  (pressed) page is reset, not the switched-to page. Previously only the
  tick-loop shape was covered. Red-tested.

- StreamController#127 reload path: check_atomic_ready_claim_reload_path asserts the per-page
  claim lock also covers the Page.py:214 reload entry point (the fix is
  broader than the issue named; it was unasserted). Red-tested: pre-fix, two
  concurrent claims via the reload trigger.

- StreamController#127 NIT: the claim probe's getter now takes a positive fast path (second
  reader reads True -> returns at once, no barrier) and the fix-present
  lock-holder wait drops from a 2.0s to a 0.5s timeout. Six checks now run in
  ~1.5s wall-clock (was ~2.4s for three).

Harness: 89/89 PASS.