feat(plugins): add service context menus and free-form canvases

[blackbartblues]

Summary

• expose native transient context menus to singleton plugin services through service.openContextMenu(request)
• anchor service menus at the cursor through compositor-independent Wayland layer-shell and xdg-shell surfaces
• add free-form declarative panel primitives: absolute positioning, x/y, zIndex, clipChildren, and input onPress
• extend drag-and-drop callbacks to onDrop(payload, target, x, y), returning the clamped target-local preview position
• add the API-gated decorated = false panel manifest option for plugin-owned fullscreen canvases
• release the combined capability bundle as Plugin API 29

Motivation

Plugins can already build regular context menus from direct panel pointer callbacks, but a singleton service invoked through IPC cannot currently open the same native menu at the cursor. This prevents keyboard-driven selection workflows such as selecting text, invoking a shortcut, and choosing a plugin action without opening a full panel.

Card-based plugins also need a real free-form canvas. Existing declarative drag and drop reports only the source payload and target ID, so a dropped card cannot persist its visual position. Absolute layout and target-local drop coordinates make sticky notes, dashboards, diagram nodes, spatial organizers, and similar plugin surfaces possible without plugin-specific core code.

The service popup path is compositor-independent. It does not query global cursor coordinates or call compositor IPC.

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring
• Build / packaging

Related Issue

Follow-up to #3899 and the panel context-menu implementation in #3906.

Testing

• just format
• full debug build
• meson test -C build-freeform --print-errorlogs — 90/90 passed
• targeted coverage for plugin bindings, lifecycle, manifest parsing, UI reconciliation, drag/drop coordinates, and context-menu popup behavior
• noctalia plugins lint against the Clipper consumer — 0 errors, 0 warnings
• live Hyprland test with the service menu at the cursor, outside-click dismissal, and a fullscreen free-form Clipper panel

Manual Coverage

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor:
• Tested with different bar positions and density settings
• Tested at different interface scaling values
• Tested with multiple monitors

The popup implementation itself uses generic Wayland protocols; compositor-specific coverage remains useful before marking the PR ready.

Screenshots / Videos

Live screenshots for the cursor menu and free-form Clipper canvas are available and will be attached before the draft is marked ready.

Checklist

• This PR is ready for review, or it is marked as Draft.
• I read and followed the relevant guidance in CONTRIBUTING.md.
• I ran just format with clang-format v22+ installed, or this PR has no code changes.
• I ran the relevant build or test commands, or explained why they were not run.
• I self-reviewed the changes.
• I checked for new warnings or errors.
• I will update end-user documentation after merge, or this PR does not change user-facing configuration or behavior.
• I added or updated assets/translations/en.json, or this PR adds no new user-facing strings.
• I did not edit non-English translation files unless this PR is explicitly for translation tooling, an import/export sync, or a maintainer-requested locale change.
• I used the existing canonical names for config keys, IPC names, paths, and identifiers.

Additional Notes

API 29 intentionally groups the service-menu and free-form-canvas contracts into one cumulative plugin API level. Existing Plugin API 28 panel context menus remain unchanged.

The documentation update belongs to the separate noctalia-docs repository. Its follow-up needs to cover the API ledger, service.openContextMenu, absolute positioning, four-argument drop callbacks, input onPress, and the decorated panel manifest key.

[blackbartblues]

2026-08-20_23-42-54-github.mp4

[blackbartblues]

@ItsLemmy Could you review it?