Add progress dialog and automatic rejoin for server-driven content installs

[Ash-bass]

Adds support for server-driven content installs with a compact modal progress dialog and automatic rejoin once installation finishes. The goal is to make the CM handoff smoother when a server asks the player to download required content, especially for car/track installs where the server already knows the correct join context, while still requiring explicit confirmation for less trusted content types.

Changes:

857cd93 + c544918:

• AcManager/Pages/Dialogs/ServerInstallProgressDialog.xaml and AcManager/Pages/Dialogs/ServerInstallProgressDialog.xaml.cs add a compact modal progress dialog for server-triggered installs, with per-item progress, success/failure states, a Hide/Cancel flow, and a manual confirmation path for non-car/track installs.
• AcManager/Tools/ArgumentsHandler.Commands.cs extends acmanager://install handling with the server-driven install UI, auto-confirm support for safe installs, rejoin state handling, and automatic rejoin after successful installation.
• AcManager/Tools/ArgumentsHandler.Race.cs uses the automatic invitation join path for reconnecting with the selected server/car/skin context after install completes.
• AcManager/Pages/Dialogs/GameDialog.xaml.cs suppresses the post-AC-close results dialog for install handoff flows so Content Manager does not show an irrelevant Practice / Try again / Replay window.
• AcManager.Tools/ContentInstallation/ContentInstallationParams.cs and AcManager.Tools/ContentInstallation/ContentInstallationEntry.cs add support for auto-confirming safe server-driven installs only when detected content is limited to cars and tracks, while leaving other content types on an explicit confirmation step.
• AcManager.Tools/ContentInstallation/ContentInstallationManager.cs adds post-install auto-rejoin state tracking used by the downloads UI and the new dialog.
• AcManager/UserControls/InstallAdditionalContentList.xaml shows the auto-rejoin status in the downloads panel.
• AcManager/AppStrings.resx and AcManager/AppStrings.Designer.cs add the new user-facing strings used by the server install/rejoin flow, including the manual-confirmation warning and confirmation button text.
• AcManager/AcManager.csproj includes the new dialog files.

Notes:

• Car and track installs can be auto-confirmed when the server provides the full rejoin context.
• Non-car/track installs are not auto-confirmed; the dialog now shows a warning and requires the player to click Confirm.
• The dialog is modal while visible, tracks only entries created by the current install request, briefly shows success before closing, and leaves failures visible so the player can see what went wrong.
• About the server download UI: I have even less experience in UI work than in general coding, so I focused on getting the flow working and reasonably clean first. It should already be acceptable, but feel free to polish it further to better match CM’s general look.

[Ash-bass]

Changes:

d148b3a:

• AcManager/Pages/Settings/SettingsContent.xaml adds a new Content > Downloading Content setting so players can disable automatic confirmation for server-driven car/track installs if they prefer to review installs manually.
• AcManager.Tools/Helpers/SettingsHolder.Content.cs stores the new ServerDownloadsAutoConfirm preference, defaulting it to enabled so the current server-handoff behavior stays unchanged unless the user opts out.
• AcManager.Tools/ContentInstallation/ContentInstallationEntry.cs updates ShouldAutoConfirmServerInstall() to respect that setting in addition to the existing server-driven autoconfirm=1 flag.
• With the setting disabled, server-driven installs still open in the same modal handoff UI, but CM waits for an explicit Confirm instead of auto-confirming car/track-only installs.