Build the production Release 0.5.0 pipeline

[CMander02]

Purpose

Implement the long-term production Release plan in verified, pushable batches. The branch remains on application version 0.4.1 until every release milestone and acceptance gate is complete; the final batch will bump all products to 0.5.0.

Current batch

• Add Pillow as a locked cross-platform runtime dependency.
• Fix image-understanding defaults and bounded image delivery.
• Add canonical server task storage, EXE worker registration/leases, long-task heartbeat and continuous archive mirroring.
• Add safe portable archive upload/download and lease-bound staged input transfer.
• Add archive thumbnail and resized-image endpoints for clients.
• Preserve referenced staging inputs while EXE workers are offline.

Validation

• uv lock --check
• Backend: 281 tests passed
• Python compileall passed
• Changed/new Python critical Ruff rules (F, E9) passed
• Secret scan passed

Next batches

Web/EXE routing UI, Android reader improvements, release identity and CI, Windows installed mode and Bootstrap, dependency/model installation center, MSI/updaters/signing, GitHub Release aggregation, server same-tag deployment, full acceptance, then the 0.5.0 version bump.