chore: add agentic development toolkit (#33)

.agents/README.md

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+# `.agents/` — harness-agnostic agentic dev toolkit
+
+Portable skills, prompts, and scripts that drive the box-box development lifecycle.
+Any harness (Claude, Codex, opencode, …) can read these — the canonical workflows
+live here, not in a tool-specific folder. The shared project context every harness
+reads is `AGENTS.md` (→ `CLAUDE.md`).
+
+## Layout
+
+```
+skills/          Codex/open agent skills: groom, write-spec, implement, review, lenses
+personas/        grill.md (base) + lens overlays (architect, …) — the interrogation voices
+prompts/         ready-spec.md (groomed spec), implement.md/review.md dispatch prompts
+lib/gh.sh        GitHub issue + Project (#2) state helpers: issue_*, set_stage/effort/priority
+lib/dispatch.sh  dispatch(): Ready issue → worktree → harness → gate → PR
+harnesses.sh     headless adapters (one fn per harness) + run_gate — the ONLY tool-specific code
+bin/dev          CLI: `dev implement <issue#> --harness <name> [--dry-run]`
+```
+
+## The lifecycle
+
+`Icebox → Research → Ready → In Progress → In Review → Done` (the Project `Stage` field).
+
+- **Groom** (interactive, Claude): `/groom <issue#>` runs a seeded grill-me → writes a
+  Ready spec into the issue body → sets Effort/Priority → leaves Stage at `Research`.
+  You review and flip to `Ready`.
+- **Implement** (any harness): `.agents/bin/dev implement <issue#> --harness <name>`
+  (or `/implement …` in Claude to supervise) → isolated worktree → runs the harness
+  headless on the spec → build gate → opens a PR → sets Stage `In Review`.
+- **Review + merge**: use the `review` skill from a harness different from the
+  implementer to create a local review packet and PR comment, then you merge.
+
+## Skills and harnesses
+
+`.agents/skills` is the canonical home for reusable workflows. Codex discovers
+repo skills from that path directly, and Claude can use the same files through
+`.claude/skills -> ../.agents/skills`. Other harnesses can read the same
+`SKILL.md` files explicitly or enter the workflow through `.agents/bin/dev`.
+Do not put canonical workflow instructions under `.claude/`; that directory is
+local adapter state.
+
+## Adding / fixing a harness
+
+Edit one function in `harnesses.sh`: `harness_<name> <workdir> <promptfile>`, running the
+tool non-interactively in `<workdir>` on the prompt. `claude`/`codex`/`opencode` are
+wired; `pi`/`cursor` are stubs — confirm their headless flags before trusting.
+
+Always `--dry-run` a new harness first: it renders the exact prompt and plan, touching
+nothing (no worktree, PR, or state change).