feat(agent): implement exec detached mode

[pacmancoder]

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[Copilot]

Pull Request Overview

This PR implements a detached execution mode for the agent's process execution functionality, allowing fire-and-forget process launches without IO redirection or active session management.

Key changes:

• Added run_detached() method to spawn processes that run independently without IO monitoring
• Refactored WinApiProcessCtx to remove the stored io_notification_tx field, passing it as a parameter instead
• Implemented console window hiding for all spawned processes (not just detached ones)

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 3 comments.

File	Description
devolutions-session/src/dvc/task.rs	Added detached mode handling in four message processors (exec_process, exec_batch, exec_winps, exec_pwsh), checking is_detached() flag and calling run_detached() instead of normal execution flow
devolutions-session/src/dvc/process.rs	Refactored WinApiProcessCtx to pass io_notification_tx as parameter; added run_impl() and run_detached() methods; implemented console window hiding via SW_HIDE flag
devolutions-session/Cargo.toml	Updated now-proto-pdu dependency to use git branch feat/exec-detached instead of crates.io version
Cargo.lock	Updated lockfile with new now-proto-pdu version from git and resolved transitive dependency versions

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[Copilot]

@pacmancoder I've opened a new pull request, #1568, to work on those changes. Once the pull request is ready, I'll request review from you.