fix(app): make per-instance launch hooks clearable

[AlexTMjugador]

This PR fixes the cleanup of per-instance launch hook overrides by bundling together several related, though technically distinct, smaller fixes:

• The HookSettings frontend page previously couldn't clear per-instance launch hooks because it failed to instruct the backend to clear the stored hook strings when no hooks were explicitly overridden. The frontend now correctly instructs the backend to clear the hooks in such cases.
• The backend incorrectly treated a Some("") launch hook as valid for launching Minecraft, even though it clearly isn't. It now correctly interprets Some(""), which may be read from the app state database for instances affected by issue I/O error: program path has no file name #3730, as equivalent to None.
• During (de)serialization of launch hook structs to the frontend, the backend also mishandled Some(""), treating it as distinct from None. This led to the storage of empty instance hook strings in the database, which triggered the issue described above.

I chose not to modify the app database schema to enforce a non-empty hook command string constraint in the profiles table because SQLite's ALTER TABLE does not support adding constraints to existing columns, and implementing such a change would require an overly complex migration for an issue that can be much simply resolved in the application layer. That said, I would definitely add such a constraint in a new schema design.

Additionally, I removed the wrap_ref_builder macro, which was only used in two places, made the code that used it harder to read, and didn't result in a reduction in lines of code.

As a result of these changes, removing per-instance launch hooks now works reliably and intuitively in the test scenario described in this issue comment.

[Copilot]

Pull Request Overview

This PR resolves issues with per-instance launch hook cleanup by ensuring that empty hook strings are treated as cleared hooks in both the frontend and backend, and removes an unused macro to simplify the code.

• Frontend now instructs the backend to clear hook overrides when not provided.
• Backend consistently filters out empty strings for hook commands via updated (de)serialization and processing logic.
• The unused wrap_ref_builder macro has been removed to improve code clarity.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/app-lib/src/util/mod.rs	Removed the unused wrap_ref_builder macro.
packages/app-lib/src/state/settings.rs	Added serde attributes to ensure empty strings are serialized as None.
packages/app-lib/src/launcher/mod.rs	Replaced macro usage with explicit mutable blocks for clarity.
packages/app-lib/src/api/profile/mod.rs	Updated hook processing to filter out empty strings for all hook types.
packages/app-lib/Cargo.toml	Added serde_with dependency for proper serialization handling.
apps/app-frontend/src/components/ui/instance_settings/HooksSettings.vue	Adjusted hook assignment to clear hooks when not overridden.

Comments suppressed due to low confidence (1)

packages/app-lib/src/api/profile/mod.rs:665

• [nitpick] Consider extracting a helper function to encapsulate retrieving a valid hook command (including filtering empty strings) since the same pattern is repeated for pre_launch, wrapper, and post_exit hooks. This would reduce duplication and improve maintainability.

.or(settings.hooks.pre_launch.as_ref()).filter(|hook_command| !hook_command.is_empty());