Add OpenIDE support

[revenant20]

Related to #115. Depends on #116.

Please review the shared-core refactoring first. View only the OpenIDE adapter changes.

Both drafts target main because cross-fork stacks are not supported. Until #116 is merged, this PR's Files changed tab also includes its changes.

Add an OpenIDE build and a PHP adapter on top of the shared-core refactoring. -PphpApi=openide uses OpenIDE 2026.2.1 and PHP for OpenIDE 0.9.4 for test discovery, running, debugging, coverage and Infection mutation testing.

Project guidance is maintained in CLAUDE.md, with AGENTS.md forwarding to it.

Runs use the project's interpreter profile. Mutation runs retain their interpreter snapshot and wait for confirmed process termination before releasing temporary reports; uncertain remote results keep their inputs and allow Stop to be retried. The build has separate outputs, dependency resolution and publishing settings, while the normal publishing matrix remains 252/262. Plugin Verifier receives the PHP dependency already resolved from the OpenIDE store.

Validation on 0c8e0315b4a80e39aaf01d7f4fa570d61bb30627:

• check buildPlugin passed on 252 and 262: 730 tests per variant, with no failures or skips. These runs used a 2 GB Kotlin compiler heap.
• check buildPlugin verifyPlugin -PphpApi=openide passed: 623 tests and a Compatible verdict on IC-262.9437.185.3, using PHP for OpenIDE 0.9.4 from its store. API deprecation and experimental-usage warnings remain.
• PhpStorm code, registrations and dependencies match the first contribution's artifacts verified on five IDE builds. Only the 252 archive's embedded release notes differ.

Live Windows/WSL acceptance remains pending.

The runtime sources, tests and build configuration at 9a7797e2b2d133e6a4b84514e6c89f671d3c50c3 are unchanged from the tested revision 0c8e0315b4a80e39aaf01d7f4fa570d61bb30627. The documentation update was checked for links and consistency with the source layout.