feat(antigravity): add client model aliases and signature bypass modes

Expose client-visible Antigravity preview model aliases while resolving
them back to upstream IDs for execution and provider discovery. Refresh
the Antigravity user agent from cached latest release metadata so model
discovery and requests track current CLI versions more reliably.

Add configurable Gemini thought signature cache modes in settings to
allow validated client-provided signatures in bypass flows while
preserving the existing stored-signature behavior by default.

Also centralize Anthropics header/version constants, enrich image model
catalog metadata with input and output modalities, add dashboard image
input support for advanced image providers, and exclude task docs from
Next standalone tracing to keep isolated builds stable.

next.config.mjs

@@ -14,6 +14,11 @@ const nextConfig = {
     },
   },
   output: "standalone",
+  outputFileTracingExcludes: {
+    // Planning/task docs are not runtime assets and can break standalone copies
+    // when broad fs/path tracing pulls the whole repository into the NFT graph.
+    "/*": ["./_tasks/**/*"],
+  },
   serverExternalPackages: [
     "pino",
     "pino-pretty",