Add webtoon MVP regression and readiness checks

[realproject7]

Parent: #197

Proposal reference: ~/z-docs/PROPOSAL-plotlink-ows-webtoon-pivot.md

Context

Because OWS stable behavior is important, this batch needs explicit regression checks around the unchanged fiction workflow and the new cartoon workflow.

Scope

• Add readiness checks for cartoon plots: clean images, overlays, final exports, upload URLs, markdown blocks, 1MB limit, and font/package size impact.
• Add regression tests for existing fiction story preview/edit/publish behavior.
• Add rollback data compatibility checks: existing story folders, publish status, local DB/config, and terminal session metadata survive switching between plotlink-ows@webtoon and plotlink-ows@1.0.33.
• Document a pre-test Claude resume id/hash capture step using ~/.plotlink-ows/data/terminal-sessions.json, with sanitized examples only.
• Document that live PTY/Claude processes do not survive restart, but stored session IDs should remain available for claude --resume.
• Add docs for local dev testing, npx plotlink-ows@webtoon, and rollback to plotlink-ows@1.0.33.
• Do not require real secrets or real private story data in tests.

Acceptance Criteria

• Test suite covers fiction regression, cartoon readiness, and rollback data compatibility expectations.
• Developer docs explain stable/global vs webtoon/npx testing, including pre-test Claude resume id/hash capture and post-rollback resume verification.
• No secrets or private paths are introduced into fixtures.
• Existing dashboard/settings/wallet pages are not changed except as explicitly required by earlier tickets.

Public Safety

This is a public repo. Do not include secrets, API keys, wallet private keys, mnemonics, auth tokens, OWS vault internals, private story drafts, or sensitive local paths in issues, PRs, logs, docs, tests, or examples.