ci: add bookmd security scanner (advisory)

[abir-vim]

Add bookmd security scanner (advisory)

This adds the self-contained org security scanner as .github/workflows/security.yml.

Advisory only — this does not block merges. On each PR it:

• runs OSV-Scanner on dependencies,
• runs a Claude (Bedrock) review across four phases (pr-review, architecture, taint, deps),
• posts a sticky Security Scanner Results comment with findings.

The in-job Security Gate ships disabled (BLOCK_ON_SEVERITY: none). To enforce later, set
BLOCK_ON_SEVERITY: critical in the workflow and add the AI security scan (phases 1-4) check to
this repo's branch protection.

Bedrock auth is via GitHub OIDC (no secrets). Optional org secrets: SCANNER_STATS_URL /
SCANNER_STATS_TOKEN (monitoring), SOCKET_API_TOKEN (Socket MCP).

🤖 Generated with Claude Code

[github-actions]

Security Scanner Results

Scope: this PR adds only a new CI workflow (.github/workflows/security.yml). No application code or dependency manifests changed, so no product-code vulnerabilities are introduced and no dependencies are made newly reachable. Phases run: pr-review, architecture, taint, deps.

Severity	Code findings
🔴 Critical	0
🟠 High	0
🟡 Medium	0
🔵 Low	3
⚪ Info	2

Findings

• ⚪ PR adds only a CI workflow; no application code or dependency changes — .github/workflows/security.yml:1
• 🔵 Workflow grants write permissions (pull-requests, issues, id-token) on pull_request events — .github/workflows/security.yml:16
• 🔵 Scanner agent is allowed Bash(gh api:*), enabling arbitrary authenticated GitHub API calls — .github/workflows/security.yml:197
• 🔵 OSV-Scanner binary fetched from latest release and executed without pinning or checksum — .github/workflows/security.yml:38
• ⚪ 94 OSV-flagged transitive packages are pre-existing, not introduced by this PR — .security-scan/osv-results.json:1

Dependencies

OSV reports 94 vulnerable transitive packages (14 critical, 40 high, 32 medium, 8 low) from an older CRA/webpack-era tree. This PR changes no manifest or lockfile, so all are pre-existing — recorded as INFO / not reachable via this change, action INFO, none BLOCK. Socket depscore enrichment was unavailable (the Socket MCP requires interactive OAuth, absent in this headless run). Recommend a separate dependency-upgrade effort.

No critical findings — no inline comments posted. Advisory only; the Security gate owns the verdict.