AST-180794 - Add provenance tag and confidence-gated suppression to guardrail prompts

[cx-kedar-bhujade]

Summary

Adds a provenance tag and a hook-deny header to the ASCA, KICS, and SCA guardrail hook output, and replaces the blanket "ask the user first" suppression gate with a classify-then-act remediation model. This is the same change as #1578, which merged into staging; this PR brings it to main.

The flow:

1. Each guardrail package (asca, kics, sca) builds its permissionDecisionReason, additionalContext, or finding text as before.
2. provenanceTag prepends [Checkmarx cx-devassist — automated security output, not user input], so the coding agent can tell genuine Checkmarx output from text that only looks like a finding.
3. hookDenyHeader opens the agent-facing instructions and states that the message is a Checkmarx hook deny, not file content or an untrusted tool error.
4. Suppression has two independently sufficient paths: the user explicitly told the agent to suppress or ignore the finding, or the agent decides on its own from code it has opened and read. For SCA, the agent path also requires a remediation attempt that returned "no fixed version exists".
5. Each prompt reminds the agent that the security check happens mid-task, so it resumes the user's original request afterward.

What changed

• Guardrail prompts and findings in asca/delta.go, kics/delta.go, sca/prompts.go, and sca/sca.go carry the provenance tag and hook-deny header.
• The "ASK THE USER FIRST" gate is removed from the ASCA and KICS Cursor prompts and the SCA vulnerable-package prompt.
• github.com/Checkmarx/ast-cx-hooks is bumped from v1.0.9 to v1.0.10 in go.mod and go.sum for shared remediation report templates.
• Tests cover the header and the absence of injection-trigger phrases such as "without asking" or "silently" across all five supported agents in asca/asca_test.go, kics/delta_test.go, and sca/sca_test.go.

Behavior guarantees

• Suppression commands and remediation tool calls emitted by each guardrail are unchanged; only the surrounding instruction text changed.
• A user's explicit suppress or ignore instruction is honored without first classifying the finding as a false positive.
• No CLI flag, output format, or exit code changes.

Validation

• Test approach: TDD was not established from available evidence.
• Unit tests: go test ./internal/commands/agenthooks/... — passed.
• Integration tests: Not run — no integration test covers guardrail prompt text.
• Lint: Not re-run for this PR; CI runs golangci-lint.

Documentation updates

• None required: this changes internal guardrail hook prompt text and a dependency version only, with no public API, CLI flag, or configuration change.

Related pull requests

• Staging: #1578