BR-4: OpenCode automatic calls via .opencode hooks

[Delqhi]

Plan: docs/plans/opencode-automatic-calls.md

Rewrite PCPM hooks: before-run -> sin-brain inject; after-run -> sin-brain reflect (async) + sin verify_tests gate. Collapse weak/legacy MCP entries to a single sin server.

Acceptance:

• before-run injects memory into context
• after-run triggers async reflect (non-blocking) + test gate
• opencode.json has exactly one sin MCP entry
  Depends on: BR-1, BR-3, SIN-Brain SB-6.