feat(cloudflare): add durable agent execution foundation

[FredKSchott]

Summary

• add one SQLite-backed Cloudflare durable submission ledger for direct HTTP, SSE, WebSocket, and detached dispatch(...) inputs
• preserve per-session FIFO ordering, fenced attempt ownership, conservative interruption handling, finite scheduled wake baton, SQL-aware deletion, and bounded lazy retention
• extract durable coordination into typed runtime modules, remove pre-1.0 compatibility bridges, align Cloudflare tooling, and document the durable execution contract

Scope

• this is the standalone Gate 1 durable-agent foundation
• workflows remain finite authored JavaScript invocations and are not made resumable
• capability G+ transcript journals, interrupted stream continuation, tool repair, watchdog scheduling, public direct replay or reattachment, and Node durability remain deferred

Accepted platform limitations

• published Agents SDK ordinary scheduled-callback exhaustion can leave pending SQL work waiting for later Durable Object activity after repeated callback failures
• authored external snapshot stores do not yet have cross-isolate revision fencing for stale whole-snapshot writes

Verification

• cd packages/runtime && pnpm run check:types && pnpm run test && pnpm run build && pnpm run test:integration:cloudflare
• cd packages/cli && pnpm run check:types && pnpm run build && pnpm run test
• cd apps/docs && pnpm run check:types && pnpm run build
• git diff --check origin/main...HEAD

Results

• runtime: 429 passed | 11 todo
• Cloudflare integration: 16 passed
• CLI: 11 passed
• docs: 66 pages built