feat(capturehttp): POST /capture REST adapter + OAuth2 + origin resolver (#53)

The HTTP door for the capture capability. Thin: authenticate → derive
trust-zone origin → decode → capture.Service → map receipt to status.

- Auth mirrors the chassis Bearer precedence (static token wins, then Dex
  JWT) but returns the resolved principal + auth path, which the chassis
  middleware hides — capture needs the principal to derive the origin.
  Depends on a small Validator interface (the chassis *JWTValidator
  satisfies it) so the JWT/origin path is testable without a live JWKS.
- OriginResolver maps principal → trust zone: static-token caller and
  allowlisted JWT subjects → sovereign; every other principal → us-nexus
  (fail safe, so the I1 gate refuses confidential by default). Principal
  and origin are server-set on the input, overwriting any body the caller
  sent.
- HTTP status: 200 all-ok / dry-run, 207 partial, 502 all-failed, 403 on
  the I1 refusal, 400 on fail-closed validation.
- Wired in main behind the same static+JWT credentials as /mcp, reusing
  the MCP server's graph-wired brain store (one implementation) and the
  classification tags (#50). Mounts only when a Gitea tracker is
  configured. Sovereign JWT principals via BRAIN_CAPTURE_SOVEREIGN_PRINCIPALS.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ingestion/internal/capturehttp/origin.go

@@ -0,0 +1,42 @@
+package capturehttp
+
+import "github.com/mathiasbq/hyperguild/ingestion/internal/capture"
+
+// OriginResolver maps an authenticated principal to its trust zone
+// (spec §4.2). The mapping is server-side and never reads caller input.
+//
+// Rules:
+//   - The static-token path is a homelab CLI caller on sovereign soil →
+//     ZoneSovereign.
+//   - A JWT principal in the sovereign allowlist → ZoneSovereign.
+//   - Any other JWT principal (e.g. claude.ai's OAuth identity, or any
+//     unrecognised subject) → ZoneUSNexus.
+//
+// The default is the strict one: an unknown principal is treated as
+// us-nexus so the I1 gate fails safe (refuses confidential), exactly as
+// an untagged classification target fails safe to confidential (#50).
+type OriginResolver struct {
+	sovereign map[string]bool
+}
+
+// NewOriginResolver builds a resolver whose JWT sovereign principals are
+// the given subjects. The static-token caller is always sovereign and
+// need not be listed.
+func NewOriginResolver(sovereignPrincipals []string) OriginResolver {
+	m := make(map[string]bool, len(sovereignPrincipals))
+	for _, p := range sovereignPrincipals {
+		if p != "" {
+			m[p] = true
+		}
+	}
+	return OriginResolver{sovereign: m}
+}
+
+// Resolve returns the trust zone for a principal. viaStatic is true when
+// the static-token auth path was taken.
+func (r OriginResolver) Resolve(principal string, viaStatic bool) capture.Zone {
+	if viaStatic || r.sovereign[principal] {
+		return capture.ZoneSovereign
+	}
+	return capture.ZoneUSNexus
+}