docs(agents): require conventional e2e workflow

[DIvanCode]

What changed

• Require Conventional Commits and matching concise PR titles in shared and Backend development guidance.
• Require the isolated Taski–Exesh e2e test after Taski/Exesh changes.
• Define when e2e scenarios must be reviewed or updated for contracts, configuration, Docker/Compose/Ansible wiring, fixtures, and submodules.
• Document the required CI shape for future cross-service e2e scenarios.

Why

The Taski–Exesh e2e gate is now part of Backend pull-request validation. The repository guidance needs to make running and maintaining that scenario a repeatable development practice.

Validation

• Parsed the e2e workflow structure.
• Checked Compose configuration and shell syntax.
• Ran Backend/Taski: go test ./....
• Ran Backend/e2e/taski-exesh/run.sh successfully through Exesh isolate.