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/groq/groq.go

@@ -0,0 +1,33 @@
+// Package groq implements the go-llm v2 provider interface for Groq
+// (https://console.groq.com). Groq hosts open-source models behind an OpenAI
+// Chat Completions-compatible endpoint, so this package is a thin wrapper over
+// openaicompat with its own defaults and per-model Rules.
+package groq
+
+import (
+	"strings"
+
+	"gitea.stevedudenhoeffer.com/steve/go-llm/v2/openaicompat"
+)
+
+// DefaultBaseURL is the public Groq OpenAI-compatible endpoint.
+const DefaultBaseURL = "https://api.groq.com/openai/v1"
+
+// Provider is a type alias over openaicompat.Provider.
+type Provider = openaicompat.Provider
+
+// New creates a new Groq provider. An empty baseURL uses DefaultBaseURL.
+func New(apiKey, baseURL string) *Provider {
+	if baseURL == "" {
+		baseURL = DefaultBaseURL
+	}
+	return openaicompat.New(apiKey, baseURL, openaicompat.Rules{
+		// Only Groq-hosted vision variants (e.g. *-vision-preview) accept images.
+		SupportsVision: func(m string) bool {
+			return strings.Contains(m, "vision")
+		},
+		// Chat completions endpoint does not accept audio input; audio is via
+		// dedicated transcription endpoints, which go-llm doesn't cover here.
+		SupportsAudio: func(string) bool { return false },
+	})
+}