fix(auth): owner allowlist trusts pass-through-authenticated callers (#59)

Allowlist.Check now takes ctx: when the caller authenticated with
their own Gitea PAT (pass-through, v0.12.0), it skips the static
GITEA_MCP_ALLOWED_OWNERS check entirely — Gitea's own permission
model already gates that caller's access more precisely than a coarse
owner-name list can. The static list still applies unchanged for the
shared static-token/JWT path, where it's the only defense against the
service token's blast radius.

Mechanical: every tool call site already had ctx in scope, so this is
a signature-only change at 41 call sites, no other tool behavior
changes. Closes the "Deferred" item from #59.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/tools/repo_search.go

@@ -53,7 +53,7 @@ func (t *RepoSearch) Call(ctx context.Context, raw json.RawMessage) (json.RawMes
 		return nil, fmt.Errorf("q is required: %w", gitea.ErrValidation)
 	}
 	if args.Owner != "" {
-		if err := t.a.Check(args.Owner); err != nil {
+		if err := t.a.Check(ctx, args.Owner); err != nil {
 			return nil, err
 		}
 	}
@@ -75,7 +75,7 @@ func (t *RepoSearch) Call(ctx context.Context, raw json.RawMessage) (json.RawMes
 			if len(parts) != 2 {
 				continue
 			}
-			if t.a.Check(parts[0]) == nil {
+			if t.a.Check(ctx, parts[0]) == nil {
 				filtered = append(filtered, r)
 			}
 		}