Follow-up to #9: Add in-bar Paste Stack deck workflow

[alvst]

What

• Shows the active Paste Stack as a single deck in Pesty's Clipboard tab.
• Adds Stack-tab collection controls plus pause, new, clear, reset, and paste actions.
• Keeps a selected stack entry visible and supports arrow keys, Return, and Delete.

Dependency

This is a draft follow-up to #9 and #29. It intentionally builds on both PRs: #9 provides Paste Stack core behavior, and #29 provides the entry previews used by this deck UI.

GitHub cannot make an upstream PR target a branch in this fork, so the current diff also contains those parent changes. After #9 and #29 merge, this branch will be rebased onto upstream main; the PR will then show only this deck-workflow commit.

Validation

• swift build
• swift build -Xswiftc -DMAS
• Tested on Apple Silicon.
• Intel Mac testing was not possible because no Intel Mac is available.

Screenshots

Demo mode; Pesty window only.