chore: prepare ScholarAIO v2.0.0 stable release

[ZimoLiao]

Summary

• promote ScholarAIO 2.0.0 from Beta to Production/Stable distribution metadata
• add the stable changelog entry covering every post-beta change from PRs refactor: remove confirmed runtime-dead code #130, Add full-instance backup and one-click restore #133, and Fix chunk filtering and harden backup integrity #134
• align the citation date, English and Chinese backup summaries, and the 2.0 upgrade guide with the stable release
• document the explicit reinstall path for beta users whose installed package already reports version 2.0.0
• harden the tag-triggered metadata gate so stable publication requires exactly one dated changelog entry, exactly one Production/Stable classifier, and an aligned valid ISO calendar date
• add a durable stable-release self-check report with the local gate evidence and remaining publication sequence

Why

The latest GitHub release is still v2.0.0-beta.1 and PyPI still serves 1.5.0. Main is now green after the beta period and the post-beta reliability work, including full-instance backup/restore, SQLite-consistent backup snapshots, bounded transfer execution, and consistent chunk paper-type filtering.

This PR closes the release-material gap before creating v2.0.0. It does not create a tag or publish an artifact.

ScholarAIO 2.0 stable highlights

• a documented 2.x public contract around ScholarAIO as an All-in-One academic harness for agents
• richer Library WebUI search, filtering, citation, and cross-platform PDF workflows
• automated cross-project agent setup and the Nature workflow bridge
• a leaner base install with MinerU cloud support isolated in its own optional extra
• full-instance backup and one-click restore for config, local secrets, data, workspaces, published outputs, and control state
• post-beta backup integrity, timeout, restore-safety, and chunk-filter correctness fixes

Upgrade impact

Users upgrading from 1.4 or 1.5 do not need another data-layout migration. Users of v2.0.0-beta.1 need an explicit reinstall because that GitHub-only beta used 2.0.0 as its installed package version; the upgrade guide now provides both PyPI and source-checkout commands.

Release gates completed

• Full suite: 1627 passed
• Ruff lint passed
• Ruff format check passed for 225 files
• Mypy passed for 147 source files
• All bundled skills passed validation
• Strict MkDocs build passed
• Stable and historical beta tag metadata checks passed
• Wheel and sdist built successfully
• Twine checks passed for both artifacts
• Fresh wheel environment passed pip check, version/classifier assertions, optional-dependency boundary check, and CLI startup

The full evidence is recorded in docs/internal/validation/reports/release-2.0.0-self-check-20260816.md.

Publication sequence after merge

1. Confirm main CI is green on the merge commit.
2. Create v2.0.0 on that exact main commit.
3. Wait for the tag-triggered Release to PyPI workflow and trusted publication to pass.
4. Verify a fresh pip install of scholaraio==2.0.0 from PyPI.
5. Publish a non-prerelease GitHub Release using the stable changelog highlights and beta reinstall warning.

Type of change

• Bug fix
• New feature / skill
• Refactoring (no behavior change)
• Documentation
• CI / tooling

Checklist

• ruff check passes
• pytest passes
• No new public API
• CHANGELOG.md updated