Move the standalone bridge worker, its Python examples, and its tests off the session and exec-stream routes and onto the unified process API.

The bridge is a thin HTTP surface over the SDK, so once the SDK drops sessions those routes map to capabilities that no longer exist. Leaving them would ship dead endpoints. This launches argv processes and recovers them by ID instead, replaces the exec and session test suites with create and process-route suites, and removes the obsolete integration harness.

Depends on the SDK process PR. No file overlap with the other migration PRs; retarget to next once the core stack merges.

Part of the unified process-execution stack.

Core stack — each builds on the previous:

•  5  Replace sessions with recoverable processes #819 — Replace sessions with recoverable processes
•  4  Rebuild container runtime around process RPC #818 — Rebuild container runtime around process RPC
•  3  Define shared process contracts and errors #817 — Define shared process contracts and errors
•  2  Build execution substrate for supervised processes #816 — Build execution substrate for supervised processes
•  1  Guard pull request quality configuration #815 — Guard pull request quality configuration
• next

Migrations — each builds on  5  #819:

• Migrate bridge clients to process resources #820 — Migrate bridge clients to process resources  👈
• Migrate examples to unified execution #821 — Migrate examples to unified execution
• Migrate E2E workflows to process handles #822 — Migrate E2E workflows to process handles
• Document unified process execution #823 — Document unified process execution
• Run execution lifecycle checks in CI #824 — Run execution lifecycle checks in CI