feat(action): add configurable no-adapter strictness

[limaronaldo]

Summary

• add a strict GitHub Action input, defaulting to true
• allow only explicit strict: false to make no-adapter discovery errors non-blocking
• keep invalid configuration and other scan errors blocking
• emit strict: true from generated CI workflows without changing the public Rust API
• cover permissive, strict, and genuine-error behavior in the Action E2E matrix

Why

Repositories that intentionally scan mixed trees may have paths with no supported AgentShield adapter. They need an explicit opt-out for that discovery condition without accidentally suppressing real scanner failures.

Verification

• cargo fmt --all --check
• cargo check --workspace --all-targets --locked
• cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
• cargo test --workspace --all-targets --locked — 422 passed
• no-default and individual feature checks
• Action/workflow YAML parsing and actionlint
• full docs/harness/bin/sensors.sh — green

[limaronaldo]

Semantic verdict: PASS

Review checklist:

• strict defaults fail-closed
• only explicit strict: false suppresses the no-adapter discovery condition
• invalid configuration and other scan errors remain blocking
• scanner exit code 2 remains exposed even when the action check is non-blocking
• generated workflows retain safe strict: true behavior
• no breaking change to the public Rust CiInstallOptions API
• composite-action E2E covers permissive, strict, and genuine-error paths
• docs match implemented semantics

No blocking findings in the remote patch. Merge remains gated on the new-head CI, especially both Action E2E platforms.