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/allowlist/allowlist_test.go

@@ -1,16 +1,36 @@
 package allowlist_test
 
 import (
+	"context"
 	"testing"
 
 	"git.d-ma.be/mathias/gitea-mcp/internal/allowlist"
+	"git.d-ma.be/mathias/gitea-mcp/internal/gitea"
 	"github.com/stretchr/testify/assert"
 )
 
 func TestAllowlistCheck(t *testing.T) {
 	a := allowlist.New([]string{"mathias", "acme"})
-	assert.NoError(t, a.Check("mathias"))
-	assert.NoError(t, a.Check("acme"))
-	assert.Error(t, a.Check("evil"))
-	assert.Error(t, a.Check(""))
+	ctx := context.Background()
+	assert.NoError(t, a.Check(ctx, "mathias"))
+	assert.NoError(t, a.Check(ctx, "acme"))
+	assert.Error(t, a.Check(ctx, "evil"))
+	assert.Error(t, a.Check(ctx, ""))
+}
+
+// A caller authenticated with their own Gitea PAT (pass-through, gitea-mcp#59)
+// is gated by Gitea's own permission model, not the MCP's static owner list —
+// otherwise a legitimate second user could never touch their own repos.
+func TestAllowlistCheckTrustsPassthroughAuthenticatedCaller(t *testing.T) {
+	a := allowlist.New([]string{"mathias"})
+	ctx := gitea.WithToken(context.Background(), "someone-elses-pat")
+	assert.NoError(t, a.Check(ctx, "someone-else"))
+}
+
+// Empty owner is a structural input error, not an authz question — still
+// rejected even on the pass-through path.
+func TestAllowlistCheckStillRejectsEmptyOwnerOnPassthrough(t *testing.T) {
+	a := allowlist.New([]string{"mathias"})
+	ctx := gitea.WithToken(context.Background(), "someone-elses-pat")
+	assert.Error(t, a.Check(ctx, ""))
 }