feat(plugins): Codex semantic memory plugin — LogosDB MCP integration (#78)

[jose-compu]

Summary

Adds plugins/codex-semantic-memory — a first-party Codex CLI plugin that wires
LogosDB's local-first MCP server into OpenAI Codex with the same automatic memory
behavior already shipping in claude-code-semantic-memory and pi-semantic-memory.

Closes #78

Changes

• plugins/codex-semantic-memory/.mcp.json — registers logosdb-mcp-server via
  a self-contained bash -c inline command; no external script dependency, works
  for both home-local (~/.codex/plugins/) and repo-local installs
• plugins/codex-semantic-memory/AGENTS.md — automatic silent behavior:
  project indexing on session start, semantic search before every response,
  turn-record persistence after every response
• plugins/codex-semantic-memory/skills/semantic-memory/SKILL.md — explicit
  commands: /memory-recall, /memory-remember, /memory-index, /memory-status
• plugins/codex-semantic-memory/scripts/logosdb-mcp-wrap.sh — standalone
  wrapper documenting LOGOS_MEMORY_MODE=global|project
• .codex-plugin/plugin.json + marketplace.json — Codex plugin manifests
• CHANGELOG updated for 0.12.0

Type of Change

• New feature (non-breaking change which adds functionality)
• Documentation update

Testing

• Manual testing performed

Plugin structure validated. .mcp.json inline command tested independently:

bash -c "MODE=${LOGOS_MEMORY_MODE:-global}; \
  if [ \"$MODE\" = project ]; then \
    export LOGOSDB_PATH=\$(git rev-parse --show-toplevel 2>/dev/null || pwd)/.logosdb; \
  else \
    export LOGOSDB_PATH=\$HOME/.codex/.logosdb; \
  fi; \
  command -v logosdb-mcp-server >/dev/null 2>&1 && exec logosdb-mcp-server || exec npx --yes logosdb-mcp-server"