docs: standardize image deployment guides

[enwaiax]

Summary

Defines and applies a reusable image-guide contract so future images enter the catalog with complete, safe, and operationally useful documentation.

This PR is stacked on #16 because the standardized Maddy guide documents the v0.9.5 paths and commands introduced there. Merge #16 first, then retarget this PR to main.

Guide standard

Adds docs/image-guide-template.md with required sections for:

• lifecycle, image version, architectures, and verification date;
• overview and deployment recommendation;
• prerequisites;
• Docker CLI and Docker Compose quick starts;
• environment variables, ports, volumes, networking, and privileges;
• first-run verification;
• logs, upgrade, backup/restore, and uninstall;
• security, troubleshooting, and known limitations.

Adds scripts/validate-image-guides.py and a required CI job. It validates all five catalog guides and rejects dangerous patterns such as recursive world-writable permissions, hard-coded aria2 RPC secrets, destructive database-reset advice, and legacy Compose commands. It also checks repository-owned Compose policy.

Guide and Compose updates

• Maddy: complete v0.9.5 deployment, DNS/TLS, verification, backup, restore, upgrade, and troubleshooting guide.
• Download Bot: fixes the wrong title, documents config fields and secrets, removes the hard-coded RPC secret, replaces host networking/PWD mounts with an isolated Compose network and relative paths.
• Netease Music Tasks: converts the page to an archived-user maintenance and credential-cleanup guide.
• X-UI: makes Moved status explicit, explains host-network risk, and removes destructive “delete the database to reset password” advice in Chinese and English.
• Firefox Send: adds the previously missing Archived guide and modernizes the historical Compose network syntax.
• RainLoop: archives the add-on guide, removes insecure permission/default-password deployment instructions, and restricts its historical HTTP binding to localhost.

All repository-owned Compose files now omit obsolete top-level version keys and use consistent logging/volume syntax.

Verification

• image guide contract: 5/5 pass;
• all repository-owned Compose files parse;
• Maddy and Download Bot Dockerfiles pass Buildx checks;
• Download Bot AMD64 image builds;
• Astro check and seven-page production build pass;
• npm production audit reports 0 vulnerabilities;
• actionlint and Python syntax checks pass;
• repository-owned guide links pass.

Publishing impact

No Docker image is published or deleted. Documentation and historical Compose behavior are made safer, but archived entries remain explicitly unsupported for new deployments.