Issuer and resource gates, retry floors, and authserver 0.2.0 alignment

[RobertoIskandarani]

Brings main up to the current development line ahead of the 0.5.0 cut. The [Unreleased] section of CHANGELOG.md is the authoritative list of what changed for a caller; this body covers the mechanics a reviewer needs.

What is in it

• Retry floor. A failed metadata or JWKS fetch opens a floor of fetchFailureBackoffSeconds (new AuthplaneClient.create() option, default 30, clamped to [1s, the cache’s refresh interval]). An unreachable authorization server used to turn every wave of verification traffic into a fresh stalling fetch.
• Freshness. AS metadata is re-read on the verification path, and a jwks_uri rotation is followed under a stable kid.
• Identifier gating. Resource and issuer identifiers are gated wherever they are consumed — absolute URL with a scheme and a host, no fragment, whitespace refused — and a non-future server expiry is ignored rather than trusted.
• Disclosure. Internal error messages and the DPoP nonce no longer reach the WWW-Authenticate challenge or the JSON body, across sdk, mcp, hono and nestjs.
• AS-hosted PRM. resource_metadata can point at a document the authorization server hosts.
• SSRF guard under Node ESM. ipaddr.js is loaded through a default import; the named import resolved to undefined under ESM interop, which disabled the guard silently.
• authserver 0.2.0. access_denied and invalid_target are typed and excluded from the circuit breaker shared with introspection. VerifiedClaims.mayAct is deprecated — the AS no longer issues may_act.
• Conformance catalog pin moves to 583a6d9.

Two deliberate carry-forwards

Both are places where this branch keeps what main already had rather than taking the development line’s copy:

1. Package versions stay on 0.4.1-dev.0, the line main was bumped to after 0.4.0. The development line is still on 0.4.0-dev.0; taking it would have walked the published dev version backwards across all six package.json files and the lockfile’s workspace snapshots.
2. One [Unreleased] bullet is condensed to a single line, matching the shape the rest of the family writes. Nothing a caller needs was dropped.

Verification

lint, typecheck and test green locally, with the conformance suites driven against the pinned catalog 583a6d9, which is what CI reads.