chore(backend): extend Makefile with audit, validation, and security targets

- Added `dep-audit`, `license-check`, `audit`, `validate-all`, and `check` targets for security and quality checks.
- Updated `.PHONY` to include new targets.
- Enhanced `help` command documentation with descriptions of the new commands.
- Updated `ARCHITECTURE.md`, `CLAUDE.md`, and `uv.lock` to reflect related changes. Upgraded dependencies where necessary.

backend/.pre-commit-config.yaml

@@ -0,0 +1,44 @@
+# Pre-commit hooks for backend quality and security checks.
+#
+# Install:
+#   cd backend && uv run pre-commit install
+#
+# Run manually on all files:
+#   cd backend && uv run pre-commit run --all-files
+#
+# Skip hooks temporarily:
+#   git commit --no-verify
+#
+repos:
+  # ── Code Quality ──────────────────────────────────────────────────────────
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.14.4
+    hooks:
+      - id: ruff
+        args: [--fix, --exit-non-zero-on-fix]
+      - id: ruff-format
+
+  # ── General File Hygiene ──────────────────────────────────────────────────
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v5.0.0
+    hooks:
+      - id: trailing-whitespace
+      - id: end-of-file-fixer
+      - id: check-yaml
+      - id: check-toml
+      - id: check-merge-conflict
+      - id: check-added-large-files
+        args: [--maxkb=500]
+      - id: debug-statements
+
+  # ── Security ──────────────────────────────────────────────────────────────
+  - repo: https://github.com/Yelp/detect-secrets
+    rev: v1.5.0
+    hooks:
+      - id: detect-secrets
+        args: ['--baseline', '.secrets.baseline']
+        exclude: |
+          (?x)^(
+            .*\.lock$|
+            .*\.svg$
+          )$