docs(release): add v1.9.0 release notes

[seakee]

Summary

Add curated Chinese and English release notes for v1.9.0.
This prepares the release branch before tagging v1.9.0.

Scope

• Frontend panel
• Manager Server
• CPA panel mode
• Full Docker mode
• Native packages / release
• Docs / Wiki
• CI / build / tooling

Changes

• Add docs/release-notes/v1.9.0-zh.md.
• Add docs/release-notes/v1.9.0-en.md.
• Document automatic usage response-header metadata migration and backfill notes.

User Impact

No user-facing behavior change from this PR. The release notes describe the v1.9.0 runtime changes already present on main.

Compatibility / Runtime Notes

• CPA panel mode: No change from this PR.
• Manager Server mode: Release notes document the v1.9.0 automatic SQLite migration and backfill behavior.
• Full Docker / native packages: No package behavior change from this PR.

Data / Security Notes

Release notes mention response-header metadata filtering for sensitive cookie, token, secret, and authorization headers. This PR does not include runtime data or secrets.

Risk / Rollback

Risk level: Low

Rollback notes:

• Revert the release notes commit before tagging if the release needs to be postponed.

Verification

• Type check
• Lint
• Tests
• Build
• Manual UI check
• Docs/link check
• Not applicable, docs-only

Commands / evidence:
Local release preflight passed: clean worktree, main matches origin/main, v1.9.0 branch/tag/release did not exist before execution.

Screenshots / Recordings

N/A, docs-only PR.

Docs

• README updated
• Wiki updated
• Release notes needed
• Not needed

Related

N/A