Add batch upgrade for multiple package selection

[Copilot]

Users updating subsets of available packages must run winget upgrade serially for each package. This adds multi-selection with sequential batch execution.

Changes

Selection State

• HashSet<usize> tracks selected package indices in Upgrades view
• Auto-cleared on view changes and post-operation

UI

• Space: toggle selection (✓ checkmark indicator)
• Shift+U: batch upgrade selected packages
• Context-sensitive status bar hints based on selection state
• Match pattern for prefix logic: (selected, marked) -> "►✓" | " ✓" | "► " | " "

Operation

pub enum Operation {
    Install { id: String, version: Option<String> },
    Uninstall { id: String },
    Upgrade { id: String },
    BatchUpgrade { ids: Vec<String> },  // Sequential execution
}

Sequential execution avoids Windows Installer mutex conflicts. Progress updates via new StatusUpdate message variant (distinct from errors).

Documentation

• README: keybindings table and usage steps
• Help overlay: Space and Shift+U shortcuts

Original prompt

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This section details on the original issue you should resolve

<issue_title>Feature request - select packages to update and batch update</issue_title>
<issue_description>I often need to update only a subset of available packages—for example, 5 out of 10 updates.

With the CLI, I run the update command for each required package one by one. It's time-consuming because I need to wait for it to complete before running the next..

With the TUI, it would be great to have the ability to select multiple packages from the list of available updates and run a batch update for them. Parallel updates are likely not possible due to Windows Installer conflicts, but a sequential batch update would work perfectly well.

Thank you!</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Feature request - select packages to update and batch update #8

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[shanselman]

Superseded by PR #20 which was merged as v0.2.0.