fix: apply the saved FPS counter when a session starts

[lippdev]

Problem

With an FPS counter style saved in Settings (Compact, Detailed, Custom or Off), starting a session showed no counter and left Afterburner's OSD on screen. It only took effect after cycling the "FPS counter" row in the session menu.

ConsoleEngine.ResolveMonitorNames rebuilt AppConfig field by field and left out FpsOverlay and FpsOverlayLayout (and ControllerLayout), so Start always saw the default external.

Fix

AppConfig.WithMonitors returns a clone with only the three monitor fields swapped, so a setting added later is carried along by itself.

Verification

• Unit tests pass locally (348), including new ones: the FPS counter survives the copy, and a reflection test that every other writable setting does too.
• The Windows build was left to CI.
• Not tested on a real session: added the manual check to docs/TESTING.md (start a session with a style already saved).

🤖 Generated with Claude Code

[pullfrog]

✅ No new issues found.

Reviewed changes The initial review covers the config-copy change, its session-start FPS overlay behavior, tests, and accompanying documentation.

• Preserve settings during monitor resolution WithMonitors clones AppConfig and swaps only the resolved monitor fields, so saved FPS overlay settings reach session startup.
• Add regression coverage Tests verify monitor replacements and preservation of the FPS settings and other writable config properties.
• Document and verify the fix Both changelogs and the manual testing checklist describe the saved-style startup scenario.

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