Release v0.1.3

Hardening

• Cleaned up public API and plugin-contract language to better match the current 0.1.x release reality
• Clarified plugin manifest compatibility handling without over-promising long-term stability
• Tightened docs around runner, plugin discovery, and recovery expectations
• Added more preservation coverage for core execution and recovery semantics
• Avoided advertising checkpoint resume for sources that do not explicitly opt into checkpoint support
• Preserved fail-closed checkpoint resume semantics for batched sink failures
• Prevented buffered pipelines from committing later pending records after a fail-closed sink write error
• Surfaced incompatible entry-point plugins in registry/CLI diagnostics instead of silently hiding them