fix: center controller content and autoplay opened files

README.md

@@ -14,11 +14,11 @@ make run
 
 The local app is `.build/Player.app`. It links the installed FFmpeg libraries; it is not a standalone distributable bundle. After upgrading FFmpeg, rebuild with `make -B`.
 
-Open a local file with **⌘O**, drop it onto the window, or use Finder's **Open With**. Files open paused. **⇧⌘W** closes the file; closing the window quits and joins the worker.
+Open a local file with **⌘O**, drop it onto the window, or use Finder's **Open With**. Successfully opened files start playback automatically, including when replacing the current file. **⇧⌘W** closes the file; closing the window quits and joins the worker.
 
 ## Playback UI
 
-The layout follows [IINA's video-first window](https://iina.io/img/screenshot.png) and the supplied screenshots: a 32-point frosted titlebar with native traffic lights and file icon, plus a dark frosted 440 × 68-point floating controller. AppKit materials blur the video beneath the chrome; muted icons, an orange volume track, a narrow seek thumb, and zero-padded time labels follow the reference. The controller starts centered with a four-percent bottom inset and keeps its relative position when the window changes size.
+The layout follows [IINA's video-first window](https://iina.io/img/screenshot.png) and the supplied screenshots: a 32-point frosted titlebar with native traffic lights and file icon, plus a dark frosted 440 × 68-point floating controller. AppKit materials blur the video beneath the chrome; muted icons, an orange volume track, a narrow seek thumb, and zero-padded time labels follow the reference. Shared vertical padding and an optical offset for symbol/slider insets balance the controller's visible top and bottom margins in both play and pause states. The controller starts centered with a four-percent bottom inset and keeps its relative position when the window changes size.
 
 Opening video fits the window to its display aspect ratio, including non-square pixels, and constrains subsequent window resizing. Fullscreen retains the normal letterboxed renderer; audio-only playback and close release the aspect constraint. Extreme ratios that cannot fit both the screen and usable controls keep a freely resizable letterboxed window.
 
@@ -49,7 +49,7 @@ Only implemented actions have controls; there are no placeholder playlist, subti
 - `Sources/Core/player.h`: the C interface and authoritative state snapshot. Playback commands enqueue work; poll state for completion. `seek_pending` is set synchronously when a seek or frame step is accepted and clears when all queued seeks/steps on that timeline finish. `player_step_frame` accepts only `-1` or `+1`, requires ready video, and publishes the selected frame's timestamp as `position`. Volume set/get is synchronous and uses a lock-free target gain. Callers own the opaque handle and must stop using it before destruction.
 - `Sources/Core/player.cpp`: single demux/decode worker, bounded buffers, timestamps, audio-master synchronization, paused previews, exact frame stepping, decoder/resampler drain, seeking, errors, and shutdown. A seek stops output and flushes all old timeline state before resuming.
 - `Sources/Core/output.hpp` and `Sources/macOS/Output.mm`: native output contract, allocation-free/nonblocking Core Audio callback and bounded audio ring, latency-aware presentation clock, retained frame mailbox, and Metal YUV conversion. The view can outlive the player safely.
-- `Sources/App/PlayerApp.swift`: MainActor state polling, file panel/Finder/drop handling, video host, AppKit glass and native slider cells, floating controls, visibility, video-fitted sizing, and native window integration.
+- `Sources/App/PlayerApp.swift`: MainActor state polling, file panel/Finder/drop handling, autoplay, video host, AppKit glass and native slider cells, floating controls, visibility, video-fitted sizing, and native window integration. The shared `PlayerModel.open` path enqueues play after an accepted open, on the new file's command timeline; the C interface still opens paused for callers that need explicit playback control.
 - `Makefile`: compiler/linker commands and app bundle construction. No generated Xcode project or additional build dependency.
 
 ## Runnable check