feat(proxy): add redeem_phantoms for by-value nonce redemption

[kipz]

Linked Issue

Closes nolabs-ai#1468

Summary

Adds redeem_phantoms to a custom_credentials route — a list of broker
credential names the route resolves from a caller-presented phantom in a request
header (by-value / proof-of-possession). A non-empty list forces interception for
the route's host; resolution is gated by credential name (not value); it composes
with a managed credential_key/auth or stands alone. JWT-shaped phantoms are
whole-token replaced so a real JWT stays 3 segments. The broker gains a
name-gated resolve_nonce_for_credentials (per-nonce name map) and the
NonceResolver trait gains a resolve_for_credentials method (default None).

Depends on (do not merge until both land in main):

• feat(tool-sandbox): add jwt-shaped nonce option for capture intercepts nolabs-ai/nono#1453 (shape: jwt capture option / jwt_phantom) — required by the
  shape-aware replacement.
• fix(proxy): add authenticated WebSocket tunneling for CONNECT/TLS-intercept routes nolabs-ai/nono#1443 (WebSocket tunneling) — required by the build_websocket_upstream_request
  call site.

This branch targets the integration base (kipz/redeem-phantoms-base = main +
the current in-flight set incl. nolabs-ai#1443/nolabs-ai#1453), so the diff is just this change.
Will rebase onto main once the dependencies land.

Test Plan

make ci clean. New unit tests: shape-aware JWT resolution (3-segment result),
opaque substring replacement, route-authoritative name gate + fail-closed,
name-vs-value across per-audience overwrites, raw-value reissue relabel, and
profile validation (composes with credential_key; rejected with
aws_auth/spiffe; empty-name rejected). Second commit makes the git-provider
tests hermetic against ambient gpg-signing.

Checklist

• An issue exists and is linked above
• All commits are signed-off, using DCO
• All new code follows the project's coding standards (CLAUDE.md) and is covered by tests
• Public-facing changes are paired with documentation updates
• Release note has been added to CHANGELOG.md if needed

Agent Disclosure

This PR was generated by an AI agent. Files consulted/changed:
crates/nono-proxy/src/{config.rs,route.rs,server.rs,token.rs,tls_intercept/{handle.rs,h2_forward.rs}},
crates/nono-cli/src/{network_policy.rs,profile/mod.rs,proxy_runtime.rs,tool-sandbox/token_broker.rs},
crates/nono-cli/data/nono-profile.schema.json. Reuses the existing NonceResolver
and CONNECT intercept dispatch; no new resolver trait, URI scheme, or consumer class.

Agent Compliance Check

• I am not prohibited from contributing under this policy
• An issue already exists (Route-gated by-value resolution of caller-presented capture nonces nolabs-ai/nono#1468)
• I disclosed that I am an agent in the issue discussion
• I described my intent and approach in the issue discussion
• I reviewed repository coding and security rules for the affected area
• I provided required attribution for reused or adapted code
• I did not use forbidden patterns such as unwrap/expect
• I used NonoError where required
• I validated and canonicalized all relevant paths
• This PR matches the approved or disclosed issue scope