docs: ship agent guides and skills from every published package

[WiktorStarczewski]

Why

Someone installs the web SDK, opens their AI agent, and asks it to build something Miden-related. Today the agent answers from training data, which for a pre-1.0 SDK is usually a version or two stale.

The blocker is that no agent auto-loads instruction files from node_modules — Claude Code walks up from cwd for CLAUDE.md, Cursor and Codex read AGENTS.md from the project, and none descend into dependencies. So this splits into a part we ship and a part that has to reach the consumer's repo. This PR is the first: the substrate.

What ships

Every published package now carries an AGENTS.md index plus a skills/ directory inside its tarball:

Package	Skills
@miden-sdk/miden-sdk	web-client-usage, frontend-pitfalls, signer-integration
@miden-sdk/react	react-sdk-patterns, testing-patterns
@miden-sdk/vite-plugin	vite-wasm-setup

Because they ship with the code, they're version-matched: a consumer pinned to 0.15 gets 0.15 guidance, not whatever HEAD says.

@miden-sdk/miden-sdk also ships its README.md for the first time — it previously published neither a readme nor any documentation, so its npm page was blank.

Each readme gains a marker-delimited block to paste into a project's root AGENTS.md, which is the part that actually makes an agent read any of this. A command to inject it automatically follows in a separate PR.

Consolidating three drifting copies

These skills already existed in agent-tools and were copied into frontend-template. Every shared skill had drifted:

skill	agent-tools	frontend-template
react-sdk-patterns	386	560
testing-patterns	237	338
frontend-pitfalls	202	186
signer-integration	196	186
frontend-source-guide	174	165
vite-wasm-setup	140	134
miden-concepts	116	110

Writing fresh files here would have made a third copy. Instead the drifted pairs are reconciled into one canonical version each, taking agent-tools as the base and merging the sections frontend-template had accumulated and never upstreamed (five in react-sdk-patterns, two in testing-patterns), with the template's directory layout generalized out.

The split is by what the knowledge is about, which turns out to be measurable — the SDK skills cite @miden-sdk/* and never crates/, the internals skills cite crates/ and never @miden-sdk/*:

• Here, shipped: anything documenting our public API. Now an API change and its documentation are the same PR, which is what stops the drift recurring.
• Here, not shipped: idxdb-patterns, wasm-bridge — internals, so they sit in .claude/skills/.
• agent-tools: everything cross-cutting — MASM, rust-sdk-*, miden-concepts, local-node-validation, slash commands.

Follow-up PRs drop the copies from agent-tools and frontend-template and point them at the published packages.

Also

• Root CLAUDE.md → AGENTS.md, with CLAUDE.md reduced to an @AGENTS.md import so Claude Code still loads it. Same for packages/react-sdk/.
• Root AGENTS.md documents the ownership boundary and the rule that a public-API change updates the shipped skill in the same PR.

Test plan

• npm pack --dry-run confirms AGENTS.md, README.md and skills/ land in all three tarballs
• CI green