Release v0.61.0

What's Changed

• Changelog for v0.60.0-preview.0 by @gemini-cli-robot in #29251
• chore(release): bump version to 0.61.0-nightly.20260908.gc647533d6 by @gemini-cli-robot in #29254
• Changelog for v0.59.0 by @gemini-cli-robot in #29253
• fix(core): preserve explicit versioned Flash model IDs by @SandyTao520 in #29252
• fix(core): prevent indirect prompt injection via build file modifications and untrusted flags by @villahernandez-coder in #29250
• fix(sandbox): harden filesystem boundaries and isolate runtime state by @diegogodinezr in #29214
• fix(core): ensure AgentLoopContext properties are preserved across object spread by @diegogodinezr in #29335
• fix(patch): cherry-pick 62364cb to release/v0.61.0-preview.0-pr-29443 to patch version v0.61.0-preview.0 and create version 0.61.0-preview.1 by @gemini-cli-robot in #29455

Full Changelog: v0.60.0...v0.61.0