Migrate version control picker to PCUI

[willeastcott]

Partially addresses #1376

Migrate version control picker from legacy UI to PCUI

Migrates the top-level UI components in the version control picker (picker-version-control.ts) from the legacy UI system to PCUI, along with corresponding CSS selector updates.

Component migrations:

• LegacyPanel → PCUI Container for the main picker, branches container, branches filter, branches panel, right side panel, and branch list item container
• LegacyTextField → PCUI TextInput for the search input
• LegacySelectField → PCUI SelectInput for the branches filter dropdown
• LegacyMenu / LegacyMenuItem → PCUI Menu / MenuItem for the branches context menu
• LegacyButton → PCUI Button for the load more button and branch dropdown buttons
• LegacyLabel → PCUI Label for branch icon, name, and ID labels

CSS updates (_editor-main.scss):

• Updated all selectors from .ui-panel.picker-version-control to .pcui-container.picker-version-control
• Flattened nested .content selectors since PCUI Containers don't use a .content wrapper
• Updated child component selectors (.ui-button → .pcui-button, .ui-label → .pcui-label, .ui-select-field → .pcui-select-input, etc.)

CSS updates (_version-control.scss):

• Updated menu selectors from .ui-menu to .pcui-menu with adjusted menu item height and label spacing
• Updated search input selectors from .ui-text-field to .pcui-text-input
• Added styling for the VC graph panel's legacy .content div
• Added user-select: text for selectable branch labels
• Removed rounded corners and hover glow from the branch dropdown button

Code quality:

• Changed var to const for 6 function-scoped variables

• Removed commented-out dead code

• Removed duplicate comments

• Fixed extra whitespace

• Consolidated PCUI component properties into constructor calls

• I confirm I have read the contributing guidelines

[Copilot]

Pull request overview

This PR migrates the Version Control picker UI from legacy Editor UI components to PCUI components, updating both TypeScript and Sass to match the new DOM/class structure.

Changes:

• Replaced several legacy UI components in the version control picker with PCUI equivalents (Container, Button, TextInput, SelectInput, Menu/MenuItem).
• Updated picker behavior to use PCUI menu show/hide events and icon-based buttons.
• Adjusted Sass selectors/styles to target PCUI classnames and layout structure.

Reviewed changes

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

File	Description
src/editor/pickers/version-control/picker-version-control.ts	Migrates picker UI elements to PCUI and updates context-menu behavior accordingly.
sass/editor/_editor-main.scss	Updates editor-wide styling for the version control picker to align with PCUI containers/components.
sass/common/_version-control.scss	Updates version control-specific styles for PCUI menus/text inputs and branch list item interactions.

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