AICTRL_DISABLE_PROJECT_CONFIG still loads AGENTS.md from .opencode/ and from directories the agent reads #250

Problem

AICTRL_DISABLE_PROJECT_CONFIG=true stops project config, plugins and the root AGENTS.md lookup, but two paths still load AGENTS.md files from the working directory as instructions:

1. packages/cli/src/session/instruction.ts:22: globalFiles() always adds <Instance.directory>/.opencode/AGENTS.md. systemPaths() loads it whenever ~/.config/aictrl/AGENTS.md (and AICTRL_CONFIG_DIR/AGENTS.md) is absent, which is the usual case on a CI runner.
2. packages/cli/src/tool/read.ts:138: InstructionPrompt.resolve() walks up from every file the agent reads and attaches any AGENTS.md it finds below the project root. This is not gated by the flag either.

In a pull request review job the working directory is the PR checkout, so the PR author can add .opencode/AGENTS.md or src/AGENTS.md and steer the run through system-level instructions. The diff itself is still untrusted model input; the gap is that these files get instruction status the caller asked to switch off.

Found in the review of #249. The README workflow now deletes AGENTS.md files before the review step as a workaround.

Expected

With AICTRL_DISABLE_PROJECT_CONFIG set, the harness loads no instruction files from the project directory: not .opencode/AGENTS.md, not nested AGENTS.md next to files the agent reads. Global files (~/.config/aictrl/AGENTS.md, AICTRL_CONFIG_DIR/AGENTS.md) and explicit instructions entries in caller config keep working.

Acceptance criteria

• globalFiles() only includes <Instance.directory>/.opencode/AGENTS.md when project config is enabled.
• InstructionPrompt.resolve() returns no project files when project config is disabled.
• Tests: with the flag set, a project containing .opencode/AGENTS.md and sub/AGENTS.md produces no instruction paths from systemPaths() and no attached instructions when reading sub/file.ts; with the flag unset, behaviour is unchanged.
• packages/cli/README.md documents which instruction files the flag disables.
• Once released, the README workflow's find . -name AGENTS.md -delete step can be dropped.