ci: cut PR runner waste and harden workflow permissions (#1226)

Pipeline audit follow-up: reduce wasted runner time on PRs and tighten CI
security, without reducing what actually gets validated.

Runner-time waste:
- Concurrency with PR-only cancel-in-progress on CI, E2E, and docker-build,
  so a new push cancels the previous commit's still-running checks. Non-PR
  runs use the unique run_id as the group, because GitHub keeps at most one
  pending run per group even with cancel-in-progress: false — a shared ref
  group could silently drop a queued master run.
- paths-ignore for docs-only changes (Markdown, docs/, .plans/, .codex/,
  .claude/) on the Electron build matrix and the E2E suites; E2E also skips
  apps/website/**. The build workflow keeps apps/website/** because its Linux
  job builds the website to verify AppStream assets. Tag pushes are
  unaffected: GitHub does not evaluate paths filters for tags.
- PRs lint affected projects only; master pushes keep the full run-many.
  Lint-global inputs (eslint.config.mjs, tools/eslint/**) now mark all 41
  lint projects affected, including the run-commands targets database and
  packaging, so the max-lines baseline cannot be widened without lint.

Hardening:
- Explicit least-privilege permissions on CI, E2E, and build-and-make; the
  create-release job keeps its job-level contents: write. The repository
  default workflow token was switched to read-only.
- New actionlint job (image pinned by digest, shellcheck at warning+), with
  the shared-anchor false positive suppressed in .github/actionlint.yaml.
  Fixed one real finding: unquoted $GITHUB_OUTPUT.
- .github/dependabot.yml: weekly cadence, minor+patch grouped per ecosystem
  (npm, GitHub Actions, Docker), majors stay individual PRs.

Docs updated: CLAUDE.md, docs/architecture/nx-workspace-boundaries.md, and
docs/architecture/validation-map.md now describe affected-lint on PRs and the
E2E path-filter exceptions.

nx.json

@@ -28,7 +28,19 @@
                 "{workspaceRoot}/.eslintrc.json",
                 "{workspaceRoot}/.eslintignore",
                 "{workspaceRoot}/eslint.config.mjs",
-                "{workspaceRoot}/tools/eslint-rules/**/*"
+                "{workspaceRoot}/tools/eslint-rules/**/*",
+                "{workspaceRoot}/tools/eslint/**/*"
+            ]
+        },
+        "lint": {
+            "cache": true,
+            "inputs": [
+                "default",
+                "{workspaceRoot}/.eslintrc.json",
+                "{workspaceRoot}/.eslintignore",
+                "{workspaceRoot}/eslint.config.mjs",
+                "{workspaceRoot}/tools/eslint-rules/**/*",
+                "{workspaceRoot}/tools/eslint/**/*"
             ]
         },
         "@nx/jest:jest": {