fix: use canonical AgentShield action repo

[limaronaldo]

Summary

Fixes the GitHub Action source/release repository after validating AgentShield in a real downstream workflow.

• generated workflows now use aiconnai/agentshield@main
• action release lookup now reads aiconnai/agentshield directly
• release asset downloads now use aiconnai/agentshield directly
• keeps the baseline-aware workflow output from AGENT-26 intact

Verification

• cargo fmt --check
• git diff --check
• cargo test ci_workflow --features full
• bash --noprofile --norc -e -o pipefail -c '<latest-version-resolution-smoke>' -> v0.8.6
• cargo run --bin agentshield -- ci install --output /tmp/agentshield-ci-canonical-smoke/agentshield.yml --baseline .agentshield-baseline.json --scan-path . --fail-on high --force