docs: add CodeWhale support (AGENTS.md native reader, zero setup) (#124)

CodeWhale reads AGENTS.md from project root per its CONFIGURATION.md —
ponytail already works with no adapter file needed. Added dedicated install
section, agent count bump (13→14), and portability table row.

Also adds Zed to the grouped instruction-only adapter list (same
mechanism: reads AGENTS.md natively).

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/agent-portability.md

@@ -19,6 +19,7 @@ to load in a given agent.
 | GitHub Copilot | `.github/copilot-instructions.md` | Repository instruction file. |
 | GitHub Copilot CLI | `.github/plugin/`, `AGENTS.md`, `.github/copilot-instructions.md`, `~/.copilot/copilot-instructions.md` | Plugin-supported (`copilot plugin marketplace add DietrichGebert/ponytail` + `copilot plugin install ponytail@ponytail`). Fallback instruction mode remains: per-project from `AGENTS.md` or `.github/copilot-instructions.md`, or globally from `~/.copilot/copilot-instructions.md` (instruction-tier, no `/ponytail` levels or hooks). |
 | Antigravity | `AGENTS.md` | Reads `AGENTS.md` at the repo root as always-on rules (like `.cursorrules`/`CLAUDE.md`); `.agents/rules/` also works for workspace rules. Instruction-tier. |
+| CodeWhale | `AGENTS.md` | Reads `AGENTS.md` from the repo root as project instructions; also reads `CLAUDE.md` and `.claude/instructions.md` as fallbacks. Instruction-tier. |
 | VS Code + Codex extension | `AGENTS.md` | The Codex extension reads `AGENTS.md` (repo root, or `~/.codex/AGENTS.md` globally). Instruction-tier; the full Codex plugin row above adds `/ponytail` levels and hooks. |
 | Kiro | `.kiro/steering/ponytail.md` | Steering rule; copy globally or into a project. |
 | Generic agents | `AGENTS.md` or `skills/*/SKILL.md` | Copy the compact rule file or load the skill files directly. |