chore: finalize changelog for v1.1.0

[RyshMan]

Problem
The release process requires a finalized versioned changelog section on the exact commit that will be tagged, but main is protected against direct pushes.

Root cause
The changelog was finalized locally for v1.1.0, but the resulting release-prep commit could not be pushed directly to main because branch protection requires changes to land via a pull request.

Fix
Promote the finalized CHANGELOG.md update through a short-lived release-prep branch so the exact changelog state can merge to main before the v1.1.0 tag is cut.

Validation

• python3 scripts/resolve_release_version.py --json
• python3 scripts/finalize_release_changelog.py --release-version v1.1.0 --json
• python3 scripts/validate_release_changelog.py --release-version v1.1.0 --json
• Full local release preflight completed successfully before opening this PR, including:
  • make prepush-full
  • go test ./... -count=1
  • make test-docs-consistency
  • make docs-site-install
  • make docs-site-lint
  • make docs-site-build
  • make docs-site-check
  • scripts/run_docs_smoke.sh
  • scripts/run_v1_acceptance.sh --mode=release
  • make test-contracts
  • scripts/validate_contracts.sh
  • scripts/validate_scenarios.sh
  • go test ./internal/scenarios -count=1 -tags=scenario
  • scripts/test_hardening_core.sh
  • scripts/test_perf_budgets.sh
  • scripts/run_agent_benchmarks.sh --output .tmp/release/agent-benchmarks-release.json
  • go test ./internal/integration/interop -count=1
  • make test-release-smoke