[management,proxy] Add per-provider skip_tls_verification for agent-network (#6630)

* [management,proxy] Add per-provider skip_tls_verification for agent-network

Let agent-network providers opt into skipping upstream TLS verification for
self-hosted / internal gateways behind a private or self-signed cert.

- provider: add SkipTLSVerification (persisted via AutoMigrate) with
  request/response mapping (nil on update preserves, explicit false clears).
- openapi: skip_tls_verification on the provider request + response; types
  regenerated.
- synthesizer: carry the flag into the llm_router route config so it reaches
  the proxy.
- proxy: llm_router sets it on the UpstreamRewrite mutation, and the reverse
  proxy applies roundtrip.WithSkipTLSVerify per selected route when forwarding
  upstream (the router dials per provider, so a per-target flag alone wouldn't
  cover it).
- tests: synthesizer route config carries the flag, router rewrite propagates
  it, and the request/response round-trip incl. update semantics.

* [e2e] Validate per-provider skip_tls_verification end to end

Add a self-signed HTTPS upstream (nginx) to the harness and a test that
provisions two providers on that same upstream — one with
skip_tls_verification=true, one false — behind one proxy + client. The
skip=true provider's chat reaches the upstream (200); the skip=false
provider's fails the TLS handshake (5xx). Same upstream, opposite outcome,
which proves the flag is honoured per provider (a single target-level flag
could not, since all of an account's providers share one synthesised
target).

* [e2e] WaitProxyPeer: require >=1 connected peer, not exact 1/1

Each proxy container registers a fresh WireGuard key and its peer is not
removed on teardown, so proxy peers from earlier tests linger in the
account as disconnected. WaitProxyPeer matched the exact string
"1/1 Connected", which failed once a second proxy-using test ran in the
same package (status "1/2"). Parse the "Peers count: X/Y Connected" line
and wait for X>=1 instead: only the live proxy can be connected, and the
caller's subsequent chat is the real end-to-end assertion. Fixes the CI
failure of TestProviderSkipTLSVerification (runs after TestProvidersMatrix).

proxy/internal/proxy/reverseproxy.go

@@ -346,6 +346,11 @@ func (p *ReverseProxy) forwardUpstream(respWriter http.ResponseWriter, r *http.R
 		r.Host = effectiveURL.Host
 		applyUpstreamHeaders(r, upstreamRewrite)
 		stripUpstreamPathPrefix(r, upstreamRewrite.StripPathPrefix)
+		// A router-selected route (e.g. agent-network provider) can opt into
+		// skipping upstream TLS verification per its provider config.
+		if upstreamRewrite.SkipTLSVerify {
+			ctx = roundtrip.WithSkipTLSVerify(ctx)
+		}
 	}
 
 	rp := &httputil.ReverseProxy{