Fix animation event editor runtime FPS scale - #9

Motivation

• The editor previously used a clip's sample rate for event frame numbers which causes exported events to be mis-timed because the runtime converts Event.frame on a fixed 30fps scale.
• When a clip has FPS != 30, adding events in the editor produces frame values that the runtime interprets at the 30fps domain, shifting event times.
• Keep the editor working in the same runtime frame domain to avoid manual user adjustments and incorrect generated AnimationData timing.

Description

• Introduced a RuntimeEventFrameRate constant set to 30 and initialized the editor's _frameRate from it instead of the clip sample rate.
• Made the FPS control a read-only IntegerField labeled Runtime Event FPS and added a tooltip that explains events are stored on the runtime 30fps scale.
• Updated ResetForClip to restore the runtime FPS instead of reading AnimationClip.frameRate so loading clips no longer changes the editor's event-frame domain.
• No other behavioral changes to event storage, curve generation, or runtime AnimationManager behavior were made.

Testing

• Ran git diff --check to validate no whitespace/conflict issues and it passed.
• Checked for a local Unity/.NET toolchain with command -v Unity || command -v unity-editor || command -v dotnet || true and none was available so an editor/compile run could not be performed in this environment.
• No automated editor/unit tests were executed in this environment.

Codex Task