docs: add compress.target job page

[a-essawy]

Reference page for the compress.target job, live since 2026-07-25.

• Real, runnable examples (SDK first, Python, cURL) with measured results
• The honest report shape: ok / infeasible_quality / infeasible_size / skipped_no_improvement
• Target shapes, tier thresholds (SSIMULACRA2 / VMAF), codec ladder + compatibility, lossless-only codecs, archive mode
• dryRun, passthrough semantics, search cost model (binary search, ~7 probes, 3x2s video sampling)
• Every claim verified against the shipped implementation and live prod runs today

Adds jobs/compress to the Jobs nav group.