test(e2e): run Gitea safely across local and CI

[ClaudiaFang]

Summary

• run disposable, secretless Gitea E2E on a fresh GitHub-hosted runner
• prevent fork PR code from reaching credentialed self-hosted GitHub/GitLab runners
• use collision-safe localhost ports and per-run temporary workdirs locally
• aggregate both E2E trust domains before downstream CI/release
• keep manual/scheduled E2E from cancelling normal push/PR required checks
• update workflow contracts, E2E documentation, and repository handoff state

Verification

• ./init.sh — lint, 56 files / 554 unit tests, build, Obsidian 1.11 compatibility
• npm run test:e2e -- --provider gitea — 3 files / 27 passed, 17 skipped
• two concurrent local Gitea runs with distinct ports/workdirs and complete cleanup
• bash -n + shellcheck + actionlint + git diff --check
• targeted real CI run 33048613679 — Gitea, aggregate gate, shared lint, Node 22/24 tests, package, and build/release all passed
• concurrent manual dispatch did not cancel the push run Gitea check after the concurrency fix
• latest SHA: Gitea and SonarCloud checks passed; unchanged GitHub/GitLab live-provider legs are still running

Closes #139

[sonarqubecloud]

Quality Gate passed

Issues
5 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[ClaudiaFang]

🎉 This PR is included in version 1.6.0 🎉

The release is available on GitHub release

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