docs(agents): close framework-parity gaps

Make the agent guidance work across frameworks that don't read AGENTS.md
natively, and make AGENTS.md self-sufficient beyond Android.

- AGENTS.md: add the Plugin (Python 3.11 aiohttp) and Desktop CLI (Node >=21,
  zero-dep) stack rules to the non-negotiables (was Android-only).
- GEMINI.md: thin pointer to AGENTS.md for Gemini CLI.
- .github/copilot-instructions.md: thin pointer + quick non-negotiables for
  GitHub Copilot.

Both shims point at AGENTS.md as the single source of truth (which links on to
CLAUDE.md for depth) so rules are single-sourced and can't drift.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/copilot-instructions.md

@@ -0,0 +1,22 @@
+# GitHub Copilot instructions — Hermes-Relay
+
+This file exists so GitHub Copilot (which reads `.github/copilot-instructions.md`,
+not `AGENTS.md`) picks up the project's agent guidance.
+
+**Read [AGENTS.md](../AGENTS.md) first — it is the single source of truth**
+for agent guidance: the entry point, the non-negotiables, and the public-repo
+writing hygiene. It links on to `CLAUDE.md` for the deep reference
+(architecture, upstream Hermes API, repository layout, per-language code style,
+the dev loop, and the Key Files map). Follow those; don't restate them here.
+
+Quick non-negotiables (the full list and rationale are in `AGENTS.md`):
+
+- **Standard path = vanilla upstream only.** The default no-plugin connection
+  must work against unmodified upstream hermes-agent; server-side needs go
+  through upstream PRs or the optional relay plugin, never fork patches.
+- **Conventional Commits**, `main`/`dev` branching — feature branches off
+  `dev`, `--no-ff` merges, tags cut from `main`.
+- **Android:** Jetpack Compose (no XML), kotlinx.serialization (no Gson),
+  OkHttp (no Ktor), `wss://` only; run `./gradlew lint` before pushing Kotlin.
+- **Public repo:** no personal names, no private infrastructure, no
+  AI/assistant self-narration in committed prose.

AGENTS.md

@@ -26,6 +26,10 @@ then `docs/spec.md` and `docs/decisions.md`.
   `--no-ff` merges, version bumps at release-prep on `dev`, tags cut from `main`.
 - **Android:** Jetpack Compose only (no XML), kotlinx.serialization (no Gson),
   OkHttp (no Ktor), `wss://` only. Run `./gradlew lint` before pushing Kotlin.
+- **Plugin (Python 3.11+):** aiohttp + asyncio (no threading), type hints
+  everywhere, structured `logging` (no `print`). **Desktop CLI (Node ≥21):**
+  zero runtime deps, strict TS + ES modules, ship compiled `dist/`. Full
+  per-language style and the dev loop live in CLAUDE.md → "Code Style".
 
 ## Public-repo writing hygiene
 

GEMINI.md

@@ -0,0 +1,13 @@
+# GEMINI.md
+
+Agent instructions for **Hermes-Relay**. This file exists so Gemini CLI (which
+does not read `AGENTS.md` natively) picks up the project's guidance.
+
+**Read [AGENTS.md](AGENTS.md) — it is the single source of truth** for every
+coding agent: the entry point, the non-negotiables (standard-path-is-vanilla-
+upstream, verify-endpoints, Conventional Commits + `main`/`dev` branching, the
+per-language stack rules), and the public-repo writing hygiene. It links on to
+`CLAUDE.md` for the deep reference (architecture, upstream Hermes API, repo
+layout, code style, the dev loop, and the Key Files map).
+
+Do not restate rules here — keep them in `AGENTS.md` so they can't drift.