Studio: Asset Browser filter (name search and type dropdown) #68

Current State

AssetBrowserPanel lists every asset with no way to narrow it. Large projects (Bistro has 636 asset files) are slow to
navigate.

Tasks

• Search box in the Asset Browser header with real-time substring (or fuzzy) matching on name and path
• Type dropdown ("All" plus every type in AssetTypeCatalog)
• Name and type filters combine; matches in sub-folders are shown flattened with their path
• Clear button and Ctrl+F to focus the search box
• Filter logic lives in Turian.Editor.Core/AssetBrowser, the panel only renders it

Acceptance Criteria

• Typing narrows the list on each keystroke without visible lag on Bistro.
• Type and name filters combine correctly and reset cleanly.

Adapted from the TurianZ (Zig) engine: turian#129