chore: migrate from opencode to trellis 0.5.0-rc.6

- Remove legacy .opencode/ directory and configuration
- Update .trellis/ to v0.5.0-rc.6 structure
- Refactor scripts: modularize common/, remove multi_agent/
- Add new common modules: git.py, io.py, log.py, types.py, etc.
- Update workflow.md and AGENTS.md
- Archive completed migration tasks

.claude/skills/trellis-meta/references/customize-local/overview.md

@@ -0,0 +1,55 @@
+# Local Customization Overview
+
+This directory is for local AI working in a user project where Trellis was installed through npm and `trellis init` has already been run. The AI should modify generated `.trellis/` and platform directories inside the project, not Trellis CLI upstream source code.
+
+## First Determine What The User Actually Wants To Change
+
+| User wording | Read first |
+| --- | --- |
+| "Change the Trellis flow / phases / next prompt" | `change-workflow.md` |
+| "Change task creation, status, archive, or hooks" | `change-task-lifecycle.md` |
+| "AI did not read context / change injected content" | `change-context-loading.md` |
+| "A platform hook is not behaving as expected" | `change-hooks.md` |
+| "Change implement/check/research agent behavior" | `change-agents.md` |
+| "Add a skill/command/workflow/prompt" | `change-skills-or-commands.md` |
+| "Adjust the project spec structure" | `change-spec-structure.md` |
+| "Add team conventions and local notes" | `add-project-local-conventions.md` |
+
+## General Operation Order
+
+1. **Confirm platform and directories**: inspect which directories exist, such as `.claude/`, `.codex/`, `.cursor/`.
+2. **Confirm the current active task**: run `python3 ./.trellis/scripts/task.py current --source`.
+3. **Read the local source of truth**: prefer `.trellis/workflow.md`, `.trellis/config.yaml`, and relevant platform files.
+4. **Modify narrowly**: edit only files related to the user's request.
+5. **Synchronize semantics**: if a shared flow changes, check whether platform entry points also need changes; if a platform entry changes, check whether `.trellis/workflow.md` still agrees.
+
+## Local File Priority
+
+| Layer | Files |
+| --- | --- |
+| Workflow | `.trellis/workflow.md` |
+| Project configuration | `.trellis/config.yaml` |
+| Task material | `.trellis/tasks/<task>/` |
+| Project specs | `.trellis/spec/` |
+| Runtime scripts | `.trellis/scripts/` |
+| Platform integration | `.claude/`, `.codex/`, `.cursor/`, `.opencode/`, and similar directories |
+| Shared skill | `.agents/skills/` |
+
+## Things Not To Do By Default
+
+- Do not edit the global npm install directory.
+- Do not edit `node_modules/@mindfoldhq/trellis`.
+- Do not assume the user has the Trellis GitHub repository.
+- Do not overwrite local files already modified by the user with default templates.
+- Do not put team project rules into public `trellis-meta`; project rules belong in `.trellis/spec/` or a local skill.
+
+## When To Inspect Upstream Source
+
+Switch to an upstream source-code perspective only when the user explicitly expresses one of these goals:
+
+- "I want to open a PR to Trellis"
+- "I want to change npm package publish contents"
+- "I want to fork Trellis"
+- "I want to modify the generation logic for `trellis init/update`"
+
+Otherwise, default to modifying local Trellis files inside the user project.