chore(security): add OSV-Scanner CI + Dependabot for github-actions only (#20037)

Adds two supply-chain controls that complement our existing pinning
strategy (full-SHA action pins, exact-version source dep pins via
uv.lock / package-lock.json) without undermining it.

.github/workflows/osv-scanner.yml
  Detection-only scan of uv.lock and the ui-tui/website package-locks
  against the OSV vulnerability database. Runs on PRs that touch
  lockfiles, on push to main, and weekly against main so CVEs
  published after merge still surface. Uses Google's officially-
  recommended reusable workflow pinned by full SHA (v2.3.5).
  Findings upload to the Security tab; fail-on-vuln is disabled so
  pre-existing vulns in pinned deps do not block merges — we move
  pins deliberately, not under CI pressure.

.github/dependabot.yml
  Scoped to github-actions only. Action pins must be moved when
  upstream publishes patches (often themselves security fixes);
  Dependabot opens a PR with the new SHA + release notes for normal
  review. Source-dependency ecosystems (pip, npm) are deliberately
  NOT enabled — automatic version-bump PRs against uv.lock /
  package-lock.json would fight our pinning strategy. CVE-driven
  security updates for source deps are enabled separately via the
  repo's Dependabot security updates setting (GitHub UI), which
  fires only when a pinned version becomes known-vulnerable.

.github/dependabot.yml

@@ -0,0 +1,44 @@
+# Dependabot configuration for hermes-agent.
+#
+# Deliberately scoped to github-actions only.
+#
+# We do NOT enable Dependabot for pip / npm / any source-dependency ecosystem
+# because we pin source dependencies exactly (uv.lock, package-lock.json) as
+# part of our supply-chain posture. Automatic version-bump PRs against those
+# pins would undermine the strategy — pins are moved deliberately, after
+# review, not on a schedule.
+#
+# github-actions is the exception: action pins (we use full commit SHAs per
+# supply-chain policy) must be updated when upstream actions publish
+# patches — usually themselves security fixes. Dependabot opens a PR with
+# the new SHA and release notes; we review and merge like any other PR.
+#
+# Security-update PRs for source dependencies (opened ONLY when a CVE is
+# published affecting a currently-pinned version) are enabled separately
+# via the repo's Dependabot security updates setting
+# (Settings → Code security → Dependabot → Dependabot security updates).
+# Those are CVE-only, not schedule-driven, and do not conflict with our
+# pinning strategy — they fire when a pinned version becomes known-bad,
+# which is exactly when we want to move the pin.
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+    open-pull-requests-limit: 5
+    labels:
+      - "dependencies"
+      - "github-actions"
+    commit-message:
+      prefix: "chore(actions)"
+      include: "scope"
+    groups:
+      # Batch routine action bumps into one PR per week to reduce noise.
+      # Security updates still open individually and bypass grouping.
+      actions-minor-patch:
+        update-types:
+          - "minor"
+          - "patch"

.github/workflows/osv-scanner.yml

@@ -0,0 +1,67 @@
+name: OSV-Scanner
+
+# Scans lockfiles (uv.lock, package-lock.json) against the OSV vulnerability
+# database. Runs on every PR that touches a lockfile and on a weekly schedule
+# against main.
+#
+# This is detection-only — OSV-Scanner does NOT open PRs or modify pins.
+# It reports known CVEs in currently-pinned dependency versions so we can
+# decide when and how to patch on our own schedule. Our pinning strategy
+# (full SHA / exact version) is preserved; only the notification signal
+# is added.
+#
+# Complements the existing supply-chain-audit.yml workflow (which scans
+# for malicious code patterns in PR diffs) by covering the orthogonal
+# "currently-pinned dep became known-vulnerable" case.
+#
+# Uses Google's officially-recommended reusable workflow, pinned by SHA.
+# Findings land in the repo's Security tab (Code Scanning > OSV-Scanner).
+# fail-on-vuln is disabled so the job does not block merges on pre-existing
+# vulnerabilities in pinned deps that we may need to patch deliberately.
+
+on:
+  pull_request:
+    branches: [main]
+    paths:
+      - 'uv.lock'
+      - 'pyproject.toml'
+      - 'package.json'
+      - 'package-lock.json'
+      - 'ui-tui/package.json'
+      - 'ui-tui/package-lock.json'
+      - 'website/package.json'
+      - 'website/package-lock.json'
+      - '.github/workflows/osv-scanner.yml'
+  push:
+    branches: [main]
+    paths:
+      - 'uv.lock'
+      - 'pyproject.toml'
+      - 'package.json'
+      - 'package-lock.json'
+      - 'ui-tui/package-lock.json'
+      - 'website/package-lock.json'
+  schedule:
+    # Weekly scan against main — catches CVEs published after merge for
+    # deps that haven't changed since.
+    - cron: '0 9 * * 1'
+  workflow_dispatch:
+
+permissions:
+  # Required by the reusable workflow to upload SARIF to the Security tab.
+  actions: read
+  contents: read
+  security-events: write
+
+jobs:
+  scan:
+    name: Scan lockfiles
+    uses: google/osv-scanner-action/.github/workflows/osv-scanner-reusable.yml@c51854704019a247608d928f370c98740469d4b5  # v2.3.5
+    with:
+      # Scan explicit lockfiles rather than recursing, so we only look at
+      # the three sources of truth and skip vendored / test / worktree dirs.
+      scan-args: |-
+        --lockfile=uv.lock
+        --lockfile=ui-tui/package-lock.json
+        --lockfile=website/package-lock.json
+      fail-on-vuln: false