* feat(mitm): add Antigravity reasoning-effort overrides
The Antigravity MITM alias mapping only ever swapped the destination model;
there was no way to override the reasoning effort Antigravity's own
thinkingConfig requested. Alias entries are now `{ model?, reasoningEffort? }`
(a legacy plain-string mapping still normalizes to `{ model }`, so no DB
migration is required). The standalone proxy (server.cjs) forwards the chosen
tier as a top-level `reasoningEffortOverride` on the intercepted request; the
antigravity->openai translator honors it ahead of its thinkingConfig-derived
guess, and an explicit "none" suppresses reasoning_effort entirely even when
Antigravity's own request asked for thinking. Reuses the existing canonical
5-tier reasoning vocabulary (`@/shared/reasoning/effortStandardization.ts`,
with max/extra aliasing to xhigh) instead of introducing a new one. The API
route validates the reasoning-effort value at the boundary and the Antigravity
tool card UI now exposes a per-model reasoning-effort selector alongside the
existing model-mapping input.
Co-authored-by: Truong Fiu <gnourtf@gmail.com>
Inspired-by: https://github.com/decolua/9router/pull/2584
* chore(changelog): fragment for #7228
---------
Co-authored-by: Truong Fiu <gnourtf@gmail.com>
