Replace v1.0 references with v1.1 in README and docs

[nficano]

ARCP v1.1 (spec/docs/draft-arcp-02.1.md) is canonical. v1.0 (spec/docs/draft-arcp-02.md) was deprecated days after publication. Even though this SDK is the reference for v1.1 features, its README badge, lede, and several doc pages still point to v1.0.

Update these files in this repo:

• README.md:5 — change badge from arcp-v1.0 to arcp-v1.1, retarget link from ../spec/docs/draft-arcp-02.md to ../spec/docs/draft-arcp-02.1.md
• README.md:7 — "Reference implementation of ARCP v1.0" → "v1.1"
• README.md:118 — reword "v1.0 is the literal string "1"" → "ARCP 1.x uses the literal \"1\" in the envelope arcp field" (the field doesn't change between revs)
• README.md:330 — "100% conforming to ARCP v1.0" → "v1.1"
• docs/README.md, docs/conformance.md:3, docs/guides/auth.md, docs/packages/runtime.md, docs/packages/client.md — drop "v1.0" wording in favor of "v1.1" (or "v1.x" where the statement is rev-agnostic)
• All links to draft-arcp-02.md → draft-arcp-02.1.md

Preserve as-is: CONFORMANCE.md (already targets v1.1 correctly with v1.0-additive notes), CHANGELOG.md (historical record).

Verify:

grep -rEn 'arcp-v1\.0|draft-arcp-02\.md([^.]|$)|conforming to ARCP v1\.0|Reference implementation of ARCP v1\.0' README.md docs/

should return zero hits.

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Audit reference: ARCP SDK Audit v1.1 (2026-05-19)