fix(load-backend): reject missing option value for backend in load-backend-contract.sh

[vaibhavsrv]

Why this matters

In ods/scripts/load-backend-contract.sh, the CLI argument parsing loop unconditionally executes shift 2 when encountering --backend. If --backend is passed as the final option without a value (for instance in automated scripts, test harnesses, or operator typos), Bash under set -euo pipefail halts with an unhandled shift count must be <= $# failure before reaching the explicit $BACKEND_ID validation check. This leaves callers with an empty diagnostic stderr and a confusing internal shell abort.

This patch adds an explicit parameter presence guard [[ $# -ge 2 ]] for --backend, writing an actionable diagnostic Missing value for argument: --backend to standard error and exiting with usage code 1. Existing options, contract file lookups, and Python environment extraction logic remain untouched.

Validation

• Baseline: Invoking bash ods/scripts/load-backend-contract.sh --backend failed with internal shell shift error and empty diagnostic output.
• Post-fix: Exits with code 1 and writes Missing value for argument: --backend to stderr; valid contracts continue to load and output expected shell exports.
• Backend contract loader suites: 2 passed. New-test Ruff, ShellCheck, and diff checks pass; new regressions wired into Linux CI.

Overlap check

• fix(pixel-inference): validate top_logprobs integer bounds #6322 (fix(pixel-inference): validate top_logprobs integer bounds) — API inference argument validation; no shell script overlap.
• fix(dashboard): guard compact resize callbacks after unmount #6317 (fix(dashboard): guard compact resize callbacks after unmount) — UI resize observer, separate layer.
• fix: guard array indexing for SERVICE_PORTS parameter expansion #6308 (fix: guard array indexing for SERVICE_PORTS parameter expansion) — Installer port parameter expansion, independent CLI helper.

Risk / AI disclosure

AI-assisted investigation, implementation and CLI regressions. This strengthens a CLI check, not runtime admission. Independent human review and platform/runtime qualification remain gates. No running configuration, deployment or upstream merge changed.

Follow-up integration evidence

Composed with #6322 at 5662f0d without conflicts. Production and test diffs passed together; backend contract loader checks remain intact.
Backlog composition was local-only (production/test diffs, excluding workflow/Makefile wiring); it is not an upstream merge or independent human approval. Declared live-review gates remain open.