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/commands/trellis/continue.md

@@ -0,0 +1,55 @@
+# Continue Current Task
+
+Resume work on the current task — pick up at the right phase/step in `.trellis/workflow.md`.
+
+---
+
+## Step 1: Load Current Context
+
+```bash
+python3 ./.trellis/scripts/get_context.py
+```
+
+Confirms: current task, git state, recent commits.
+
+## Step 2: Load the Phase Index
+
+```bash
+python3 ./.trellis/scripts/get_context.py --mode phase
+```
+
+Shows the Phase Index (Plan / Execute / Finish) with routing + skill mapping.
+
+## Step 3: Decide Where You Are
+
+`get_context.py` shows the active task's `status` field. Route by `status` + artifact presence:
+
+- `status=planning` + no `prd.md` → **1.1** (load `trellis-brainstorm`)
+- `status=planning` + `prd.md` exists + `implement.jsonl` not curated (only the seed `_example` row) → **1.3**
+- `status=planning` + `prd.md` + curated `implement.jsonl` → **1.4** (run `task.py start` to enter Phase 2)
+- `status=in_progress` + implementation not started → **2.1**
+- `status=in_progress` + implementation done, not yet checked → **2.2**
+- `status=in_progress` + check passed → **3.1**
+- `status=completed` (rare; usually archived immediately) → archive flow
+
+Phase rules (full detail in `.trellis/workflow.md`):
+
+1. Run steps **in order** within a phase — `[required]` steps must not be skipped
+2. `[once]` steps are already done if the output exists (e.g., `prd.md` for 1.1; `implement.jsonl` with curated entries for 1.3) — skip them
+3. You may go back to an earlier phase if discoveries require it
+
+## Step 4: Load the Specific Step
+
+Once you know which step to resume at:
+
+```bash
+python3 ./.trellis/scripts/get_context.py --mode phase --step <X.X> --platform claude
+```
+
+Follow the loaded instructions. After each `[required]` step completes, move to the next.
+
+---
+
+## Reference
+
+Full workflow, skill routing table, and the DO-NOT-skip table live in `.trellis/workflow.md`. This command is only an entry point — the canonical guidance is there.