Release v0.51.0

What's Changed

• Changelog for v0.50.0-preview.1 by @gemini-cli-robot in #28150
• Fix no_proxy test by @jerrylin3321 in #28131
• chore(release): bump version to 0.51.0-nightly.20260625.g3fbf93e26 by @gemini-cli-robot in #28151
• Vertex base url update by @DavidAPierce in #28145
• fix(security): enforce case-insensitive sensitive path blocklist and vscode hitl by @luisfelipe-alt in #27966
• fix(core-tools): resolve defensive path resolution for at-reference files and fix macOS tests by @luisfelipe-alt in #28053
• feat(caretaker): implement Cloud Run webhook ingestion service by @chadd28 in #28015
• fix(core): resolve symbolic link directory escape in memory import processor by @luisfelipe-alt in #28233
• feat(caretaker): egress cloud run service skeleton by @chadd28 in #28167
• fix(sandbox): make ~/.gitconfig read-only in the macOS sandbox by @ompatel-aiml in #28221
• fix(core): preserve escape sequences in string literals for modern models by @luisfelipe-alt in #28299
• fix(core): strip thoughts from scrubbed history turns and resolve thought leakage by @amelidev in #27971

Full Changelog: v0.50.0...v0.51.0