Implement accessibility API context for enhancement

[poodle64]

Description

src-tauri/src/enhancement/context.rs:66 has a TODO to implement active window context using accessibility APIs.

Currently returns empty context. Should use:

• macOS: Accessibility APIs to get focused app name, document title
• Linux: Platform-specific methods (D-Bus, AT-SPI)

Acceptance Criteria

• Get active application name on macOS via accessibility APIs
• Get document/window title where available
• Graceful fallback to empty context if permissions denied

[m13v]

for macOS accessibility context, the pattern we use is: get the frontmost app PID from NSWorkspace, create an AXUIElement for that app, then walk the focused window to extract the document title and app name. the key APIs are AXUIElementCreateApplication(pid) and AXUIElementCopyAttributeValue with kAXFocusedWindowAttribute, then kAXTitleAttribute on the window element. the permission check is AXIsProcessTrustedWithOptions, pass kAXTrustedCheckOptionPrompt: false to check without triggering a dialog. when permissions are denied, return the app name from NSWorkspace (no permission needed) but skip the window title. most apps expose meaningful titles through AX, but some Electron apps return empty strings so always have the fallback.

[m13v]

our MCP server that implements the AXUIElement focused window + app context pattern for macOS: https://github.com/mediar-ai/mcp-server-macos-use/blob/main/Sources/MCPServer/main.swift

shows permission checking, tree walking, element attribute reading, and graceful fallback when accessibility permissions are not granted.