CLI Proxy API 6.8.38 አውርድ

Changelog
- 8aa2cce8c5634613dfd28d50140d27d142e37cc8 Merge PR #1735 into dev with conflict resolution and fixes
- 2a4d3e60f3806ec9576582bb4fbd06699614962f Merge remote-tracking branch 'upstream/dev' into dev
- 4040b1e766e072ea7ec032a32186b2ea0bb12993 Merge remote-tracking branch 'upstream/dev' into dev
- d6cc976d1f55ab4f59756ee8db04d16e6b134a06 chore(executor): remove unused header scrubbing function
- f3c164d34523e9ece5130c16d4c2d79e80a12371 feat(antigravity): update to v1.19.5 with new models and Claude 4-6 migration
- 846e75b89319214fb9fa6fbea8d52f5af427cd8e feat(gemini): route gemini-3.1-flash-image identically to gemini-3-pro-image
- 8f97a5f77c93eebb3e98ff68d5ff5734611edb64 feat(registry): expose input modalities, token limits, and generation methods for Antigravity models
- 5dc1848466eddc8f9b2f34dcb45eb31cecc342fb feat(scrub): add comprehensive browser fingerprint and client identity header scrubbing
- 2baf35b3ef5b441154b61a11afa3a78c00a9b487 fix(executor): bump antigravity UA to 1.19.6 and align image_gen payload
- 9370b5bd044b7f4952f832f1ab286aa667aa9a6c fix(executor): completely scrub all proxy tracing headers in executor
- abb51a0d93732b85cdc74f9c82ebadef44f3cc32 fix(executor): correctly disable http2 ALPN in Antigravity client to resolve connection reset errors
- c8d809131bc45b790114ba47914de370fb7b8dce fix(executor): improve antigravity reverse proxy emulation
- 8b5af2ab8444e7d07e1e65c001b7f1598e984e97 fix(executor): match real Antigravity OAuth UA, remove redundant header scrubbing on new requests
- 9491517b2664d20ef05e7d2ae9c96865187bf2c5 fix(executor): use singleton transport to prevent OOM from connection pool leaks
- 68dd2bfe82656b8fbda7f001b477ddd6f88c79d7 fix(translator): allow passthrough of custom generationConfig for all Gemini-like providers
- dd71c73a9f4d6960e55929f2f7b97b102804279a fix: align gemini-cli upstream communication headers
- 660bd7eff59bc815e856e9744401030c9b49033d refactor(config): remove oauth-model-alias migration logic and related tests
- d887716ebd7db9e3620bd917015ebe2a569e9578 refactor(executor): switch HttpRequest to whitelist-based header filtering
- 914db94e79285e3fd2b8f235a349c72f97fa6601 refactor(headers): streamline User-Agent handling and introduce GeminiCLI versioning
- fc0257d6d9da96de34ff30fd97702ee3f6353415 refactor: consolidate duplicate UA and header scrubbing into shared misc functions
- b907d21851af9031264b5b5e7380a3b430e68f7c revert(executor): revert antigravity_executor.go changes from PR #1735