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/issue_comment.go

@@ -50,7 +50,7 @@ func (t *IssueComment) Call(ctx context.Context, raw json.RawMessage) (json.RawM
 	if err := parseArgs(raw, &args); err != nil {
 		return nil, err
 	}
-	if err := t.a.Check(args.Owner); err != nil {
+	if err := t.a.Check(ctx, args.Owner); err != nil {
 		return nil, err
 	}
 	if args.Number < 1 {