feat: opencode zen adapter + first-run config generation, fix stats/stream bugs

- adapters/opencode.lua: opencode.ai zen free pool adapter — sends the
  opencode client User-Agent (zen fingerprints clients by UA; non-official
  clients hit FreeUsageLimitError); pairs with api_key: public
- config: no config file ships in the repo; first run generates a default
  config at the -config path with a random admin key, loopback listen and a
  keyless zen source (config.EnsureDefault); remove config.example.yaml
- lua: seed bundled adapters from the embedded FS instead of a hardcoded
  name list
- ui: widen model kind select (chat was clipped to 'cha')
- phase 5 bugfixes: stats ms/s bucket mixing, cleanScopes nil, ctx.Err
  guards, direct-path ModelAvailable, empty stream body failure,
  bestImageModel rewrite, transform failure recording, Core.mu, timer,
  effective model for tool-calls

internal/gateway/stats_test.go

@@ -6,6 +6,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 )
 
 func TestStatsByStatus(t *testing.T) {
@@ -91,18 +92,21 @@ func TestAuditRotationRecords(t *testing.T) {
 func TestLoadAuditFullReplay(t *testing.T) {
 	dir := t.TempDir()
 	path := filepath.Join(dir, "audit.jsonl")
+	// timestamps relative to now: buckets are whole unix hours, so window
+	// assertions must not depend on the minute-of-hour of the test run.
+	now := time.Now()
 	lines := []string{
 		`{"obj":"access","time":1699999999000,"key":"k","method":"GET","path":"/api/stats","status":200}`,
-		`{"time":1700000000000,"key":"k","type":"chat","model":"m","source":"s","prompt_tokens":100,"completion_tokens":50,"latency_ms":10,"ok":true,"status":200}`,
+		fmt.Sprintf(`{"time":%d,"key":"k","type":"chat","model":"m","source":"s","prompt_tokens":100,"completion_tokens":50,"latency_ms":10,"ok":true,"status":200}`, now.Add(-65*time.Minute).UnixMilli()),
 		`{this is not valid json`,
-		`{"time":1700003600000,"key":"k","type":"stream","model":"m","source":"s","prompt_tokens":200,"completion_tokens":20,"latency_ms":20,"ok":false,"status":503}`,
+		fmt.Sprintf(`{"time":%d,"key":"k","type":"stream","model":"m","source":"s","prompt_tokens":200,"completion_tokens":20,"latency_ms":20,"ok":false,"status":503}`, now.Add(-30*time.Minute).UnixMilli()),
 		"garbage-not-json\n",
-		`{"time":1700007200000,"key":"k","type":"chat","model":"m2","source":"s","prompt_tokens":7,"completion_tokens":3,"latency_ms":5,"ok":true,"status":200}`,
+		fmt.Sprintf(`{"time":%d,"key":"k","type":"chat","model":"m2","source":"s","prompt_tokens":7,"completion_tokens":3,"latency_ms":5,"ok":true,"status":200}`, now.Add(-30*time.Minute).UnixMilli()),
 	}
 	loaded := strings.Join(lines, "\n") + "\n" + strings.Repeat("x", 1<<18) + "\n"
 	// oversized row at the END proves the scanner tolerates >64KB lines and
 	// still finishes the replay instead of truncating silently.
-	loaded += `{"time":1700010800000,"key":"k","type":"chat","model":"m","source":"s","prompt_tokens":1,"completion_tokens":1,"latency_ms":1,"ok":true,"status":200}` + "\n"
+	loaded += fmt.Sprintf(`{"time":%d,"key":"k","type":"chat","model":"m","source":"s","prompt_tokens":1,"completion_tokens":1,"latency_ms":1,"ok":true,"status":200}`, now.Add(-time.Minute).UnixMilli()) + "\n"
 	if err := os.WriteFile(path, []byte(loaded), 0644); err != nil {
 		t.Fatal(err)
 	}
@@ -121,9 +125,24 @@ func TestLoadAuditFullReplay(t *testing.T) {
 	if len(s.recs) != 4 {
 		t.Fatalf("ring must hold only real requests, got %d rows: %#v", len(s.recs), s.recs)
 	}
-	// quota window rebuilt from full history
-	if w := s.WindowTokens("m", "s", hourSec); w != 372 {
-		t.Fatalf("window tokens want 372, got %d", w)
+	// quota window rebuilt from full history. All-time and multi-hour windows
+	// must see everything; a 1h window must NOT return all records (the old
+	// ms/seconds unit bug made any sec>0 window return everything), and must
+	// always include the row written one minute ago (current hour bucket).
+	if w := s.WindowTokens("m", "s", 0); w != 372 {
+		t.Fatalf("all-time window want 372, got %d", w)
+	}
+	if w := s.WindowTokens("m", "s", 3*hourSec); w != 372 {
+		t.Fatalf("3h window want 372, got %d", w)
+	}
+	if w := s.WindowTokens("m", "s", 24*hourSec); w != 372 {
+		t.Fatalf("24h window want 372, got %d", w)
+	}
+	if w := s.WindowTokens("m", "s", hourSec); w < 2 || w >= 372 {
+		t.Fatalf("1h window want [2,372), got %d", w)
+	}
+	if w := s.WindowTokens("m2", "s", 24*hourSec); w != 10 {
+		t.Fatalf("m2 24h window want 10, got %d", w)
 	}
 	// by_status only from requests (200 x3, 503 x1) — access line must not count
 	if st := s.byStatus[200]; st == nil || st.Reqs != 3 {