Rebase and land #932: client-executed tools + HITL approval flow

[wishborn]

Upstream prism-php#932 (client-executed tools + human-in-the-loop tool approval, answering upstream issue prism-php#921) was deferred from v0.104.0: it touches all 28 provider Text/Stream/Structured handlers, was authored ~4 months before Batches 1–3 landed (conflicts with prism-php#996, prism-php#1009, prism-php#952, prism-php#954, prism-php#965, prism-php#1018, prism-php#951 among others), and its head commit is WIP-marked ('stash changes').

Plan:

• Extract the core design (client tool markers, approval flow events, BroadcastAdapter) from the PR
• Reimplement against current main, provider by provider, starting with Anthropic + OpenAI
• Port its 106 test files' coverage where still applicable
• Coordinate with the Reverb-based sandbox for a live HITL demo

[wishborn]

Phase 1 shipped in v0.106.0: core value objects/events/broadcast, Tool::clientExecuted() + requiresApproval(), deny-by-default resume path, wired for Anthropic + OpenAI Text/Structured, 39-test unit suite ported from prism-php#932.

Remaining for phase 2:

• Streaming emission (ToolApprovalRequestEvent in provider streams + finish-event flow; resolve-with-StreamState path)
• Roll out loop-stop wiring to remaining providers (Gemini, Groq, Mistral, DeepSeek, Ollama, OpenRouter, xAI, Z, Qwen, Azure, Requesty, ChatCompletions handlers)
• Docs page (core-concepts) for client tools + approval flow
• Reverb-based live demo in the docs site app

[wishborn]

Phase 2 shipped in v0.107.0: HITL rolled out to all Text/Structured handlers (13 more providers incl. ChatCompletions), streaming emission for Anthropic + OpenAI (approval events + ToolCalls stream end + resume-at-start), and the core-concepts docs page.

Remaining:

• Streaming emission for the other providers' streams
• Reverb live approval demo in the docs site app

[wishborn]

All items complete:

• ✅ Core + Anthropic/OpenAI Text+Structured (v0.106.0)
• ✅ All providers Text/Structured + An/OAI streaming + docs page (v0.107.0)
• ✅ Streaming for all remaining provider streams (v0.108.0)
• ✅ Reverb live approval demo shipped in the docs site app at /demo/hitl — real Anthropic stream broadcast per-run over Reverb, live approval card, approve/deny resume. Requires ANTHROPIC_API_KEY in the app env.

Upstream prism-php#932's feature set is now fully landed, rebuilt against current main with deny-by-default approvals and a ported 39-test suite plus stream fixtures.