feat: add DeepSeek, Moonshot, xAI, Groq, Ollama; drop v1; migrate TUI to v2

Five OpenAI-compatible providers join the library as first-class constructors
(llm.DeepSeek, llm.Moonshot, llm.XAI, llm.Groq, llm.Ollama). Their wire-level
implementation is shared via a new v2/openaicompat package which is the
extracted guts of the old v2/openai provider; each provider supplies its own
Rules value to declare per-model constraints (e.g., DeepSeek Reasoner rejects
tools and temperature, Moonshot/xAI accept images only on *-vision* models,
Groq rejects audio input). v2/openai itself becomes a thin wrapper that sets
RestrictTemperature for o-series and gpt-5 models.

A new provider registry (v2/registry.go) exposes llm.Providers() and drives
the TUI's provider picker so adding a provider in future is a single-file
change.

The TUI at cmd/llm was migrated from v1 to v2 and moved to v2/cmd/llm. With
nothing else depending on v1, the v1 code at the repo root (all .go files,
schema/, internal/, provider/, root go.mod/go.sum) is deleted.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

v2/moonshot/moonshot_test.go

@@ -0,0 +1,33 @@
+package moonshot_test
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"gitea.stevedudenhoeffer.com/steve/go-llm/v2/moonshot"
+	"gitea.stevedudenhoeffer.com/steve/go-llm/v2/openaicompat"
+	"gitea.stevedudenhoeffer.com/steve/go-llm/v2/provider"
+)
+
+func TestNew_Basic(t *testing.T) {
+	if p := moonshot.New("key", ""); p == nil {
+		t.Fatal("New returned nil")
+	}
+}
+
+func TestRules_NonVisionModelRejectsImages(t *testing.T) {
+	p := moonshot.New("key", "")
+	req := provider.Request{
+		Model: "moonshot-v1-8k",
+		Messages: []provider.Message{{
+			Role:   "user",
+			Images: []provider.Image{{URL: "a"}},
+		}},
+	}
+	_, err := p.Complete(context.Background(), req)
+	var fue *openaicompat.FeatureUnsupportedError
+	if !errors.As(err, &fue) || fue.Feature != "vision" {
+		t.Fatalf("want FeatureUnsupportedError(vision), got %v", err)
+	}
+}