Spec mandates @ references in the Phase Files table; every template and example uses backticked paths

[TGPSKI]

What changed

Two spec lines required a convention no template, example, or pattern doc in this repo follows.

• SKILL.md:148 — "lists all phases with @ references" → "lists all phases as backticked relative paths, one level deep from the router". Matches templates/multi-phase-router/router.md:83-88 and all four examples.
• SKILL.md ### Router Rules — new rule: the router names the phase file by relative path and instructs the agent to read it. The read is the load; a bare path is not a directive to load anything.
• CONTRIBUTING.md:72 — "all internal @-references resolve to existing files" → "all internal links resolve to existing files".
• README.md:67 — notes that @onboard-chart/SKILL.md is a prompt mention that attaches the router to the conversation, distinct from how a router references its phase files. Prevents the next reader from "fixing" it.

Why

@path is a CLAUDE.md-family import mechanism — imported files expand into context at launch, recursive to four hops — not a markdown convention. SKILL.md is not a memory file, so @ there is inert text: a path with a decorative sigil. Import parsing also skips code spans, so the spec's own backticked `@` would not import anything even in a CLAUDE.md.

Two failure modes if the spec were followed literally:

1. An agent reads @ as "load this now" and pulls every phase file at router time, defeating the progressive disclosure the router exists to provide.
2. If a router's text reaches a CLAUDE.md through the documented @AGENTS.md import pattern, the phase files genuinely expand at launch.

Anthropic's skill-authoring guidance uses plain markdown links for bundled files and says to keep references one level deep from SKILL.md — the router → references/ shape this repo already uses. No AGENTS.md-family spec defines an import syntax, and Cursor's @ is a chat-composer mention with different resolution rules.

Acceptance

SKILL.md and CONTRIBUTING.md describe the convention the templates and all four examples already use.

Met. SKILL.md:148 now says "backticked relative paths, one level deep from the router", matching templates/multi-phase-router/router.md:83-88, examples/kubernetes-onboarding/onboard-service/SKILL.md:74-79, and the terraform-aws-account, ansible-inventory, and contributor-access examples. CONTRIBUTING.md:72 no longer asks reviewers to verify references that do not exist.

No template or example file changes — they are already correct. A diff that touches templates/ or examples/ means the fix went the wrong direction.

Met. git diff --name-only returns exactly CONTRIBUTING.md, README.md, SKILL.md. git diff --name-only -- templates/ examples/ is empty.

README.md prompt-invocation syntax is unchanged.

Met. README.md:6 (User: @onboard-service/SKILL.md) is untouched. README.md:67 keeps `@onboard-chart/SKILL.md` verbatim; only explanatory prose was appended.

Remaining @ file-references after the change, per the issue's grep — the two README invocations plus examples/contributor-access/grant-access/references/phase-02-access.md:95 (@{github-username}, unrelated mechanism), all expected.

Closes #6