v0.3.5

Simulation ("mock") engine is now off by default

The mock engine is gated behind a cargo feature that is not in the default set, so cargo build, cargo install and every release binary can never simulate.

Why: /v1/models advertises the real provider catalog, while the simulator only knows its own built-in list (gpt-4o, claude-sonnet-4-6). With mock reachable, every advertised model id 404'd at the simulator — the one configuration where a listed model routes nowhere. One real routing path is worth more than a second one.

What is overridden (all four are now inert in a default build):

• OPENPROXY_DEV_MOCK=1 environment variable
• the stored devMockAll setting
• a sim-stub- connection id
• the x-openproxy-sim: mock request header

The code is kept, not deleted (src/core/simulation/, ~3.2k lines). Rebuild with --features simulation to get the engine back; its tests live behind the same flag.

Closes beads sim-11 / sim-20. Divergence from 9router is documented in docs/parity-9router.md.

Full Changelog: v0.3.4...v0.3.5