feat: OpenAI, Anthropic, and native-Ollama providers + media pipeline

Phase 3:
- provider/openai: Chat Completions for OpenAI + compat endpoints (SSE
  streaming with by-index tool-call assembly, response_format json_schema,
  legacy max_tokens option, reasoning_effort)
- provider/anthropic: Messages API (tool_use/tool_result, GA structured
  output via output_config.format, full SSE event parser, 529 transient)
- provider/ollama: one native /api/chat client behind the ollama,
  ollama-cloud, and foreman built-ins (presets; NDJSON streaming tolerant
  of foreman's buffered single-object responses; object tool arguments;
  format-schema structured output; think mapping)
- media/: capability normalization (sniff, downscale, transcode, byte
  ladder, ErrUnsupported), wired into the chain executor per target with
  penalty-free advance past incapable elements
- registry: real provider + scheme wiring, WithHTTPClient option, required
  env-foreman TLS chat round-trip test
- ADR-0009 multimodal strategy, ADR-0010 tools/structured mapping; README
  matrix + CLAUDE.md synced

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/adr/README.md

@@ -12,3 +12,5 @@ One decision per file, append-only; supersede rather than rewrite.
 | [0006](0006-health-and-backoff.md) | Model health tracking and backoff | Accepted |
 | [0007](0007-dependency-policy.md) | Dependency policy — stdlib-first, hand-rolled REST clients | Accepted |
 | [0008](0008-chain-semantics.md) | Failover-chain execution semantics | Accepted |
+| [0009](0009-multimodal-strategy.md) | Multimodal strategy — normalize per target, enforce at provider | Accepted |
+| [0010](0010-tools-structured-output-mapping.md) | Tools and structured output — canonical shape, native mappings | Accepted |