Vision backends: any OpenAI-compatible endpoint, including local models

The Anthropic key was the last hard gate for other users. extract's
VisionFn seam gains a second factory speaking the chat-completions
format — OpenAI, OpenRouter, or a local runtime (Ollama, LM Studio,
llama.cpp, vLLM) via config.toml: vision_provider, vision_base_url,
and vision_key_env ("" = keyless local endpoint, no Authorization
header sent). Anthropic stays the default. load_config rejects unknown
providers loudly, the pipeline page's credentials warning follows the
configured provider (a keyless local endpoint warns about nothing),
and config.toml + README document the local-model trade honestly:
weaker spine reading means a longer proofread pass, which the shaky-
read workflow absorbs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jXZFSTZQKzAC8fqpWSz9g

config.toml

@@ -5,3 +5,10 @@ photos_dir = "photos"
 data_dir = "data"
 model = "claude-sonnet-5"
 rate_limit_seconds = 2.0
+
+# Vision backend. The default ("anthropic") reads ANTHROPIC_API_KEY.
+# "openai-compatible" covers OpenAI, OpenRouter, and local runtimes:
+#   vision_provider = "openai-compatible"
+#   vision_base_url = "http://localhost:11434/v1"   # e.g. Ollama
+#   model = "qwen2.5vl"                             # a vision-capable model
+#   vision_key_env = ""                             # local: no key needed