feat: introduce portable plugin engine V2

[Devin-AXIS]

What changed

• introduces a shared, engine-neutral plugin package V2 contract and server adapter boundary
• moves common package capabilities into top-level skills/ and mcp/, while keeping OpenCode-specific assets under engines/opencode/
• migrates the maintained example packages and documentation to the V2 manifest
• keeps package-owned Skills and MCP services grouped inside their plugin package in the Extensions UI
• removes the pre-release V1 lifecycle compatibility path so the active implementation is V2-only

Why

The previous package shape exposed OpenCode-specific directories as the platform contract. This change makes iPolloWork's capability package the stable contract and leaves each agent engine behind an adapter, allowing future engines without changing the product-facing plugin model.

It also fixes the regression where package relationships could be empty and package-owned capabilities such as Figma or Notion appeared as standalone extensions.

Compatibility

Pre-release V1 local lifecycle state is intentionally not migrated. Existing test installations can reset or reinstall their local plugin packages; fresh state starts directly on schema V2.

Validation

• server plugin lifecycle tests: 15 passed, 145 expectations
• app extension projection tests: 18 passed, 117 expectations
• server and app TypeScript checks passed
• maintainability audit passed with no warnings
• git diff --check passed
• live development runtime health passed on v0.21.1
• authenticated package and catalog requests returned 200; 11 package cards rendered without flattening package-owned Skills

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve shared package-name registrations

When a packageName capability matches a plugin already registered through the plugins API or by another package, installation merely adopts the existing normalized spec because addPlugin deduplicates it, but disabling, updating, or uninstalling this package unconditionally calls removePlugin, which deletes that shared registration (plugins.ts:89-107). The original owner then silently loses its runtime plugin; track ownership/reference counts or reject colliding package-name capabilities before removing them.

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