[feature] Claude Code integration: OpenContext MCP server configurable via `opencontext` CLI, publishable as a Claude Code plugin

[Peefy]

Problem

Claude Code is a primary agent harness for many OpenContext users, but today integrating OpenContext means manual plumbing such as:

claude mcp add opencontext -s user -- opencontext mcp \
  --embedding-provider local --memory-backend sqlite-vec

...and separately recreating any skill/command files by hand. There is no managed install path from our side, no way to keep the config in sync when providers/backends change, and no packaged slash-command surface.

Meanwhile the repo already ships plugins/dsh-opencontext for the DeepSeek Harness — Claude Code deserves the same treatment (see also the sibling Codex CLI request in #20).

Proposed solution

Again, two installation paths:

Path A — configure from the opencontext CLI

pnpm add -g @melandlabs/opencontext

# Writes the MCP registration (project .mcp.json or user scope, selectable via --scope)
opencontext mcp install --target claude-code [--scope project|user]

# Shell out to `claude mcp add ...` when the Claude Code CLI is detected,
# otherwise write JSON directly. Idempotent updates only.

# Health checks afterwards:
opencontext doctor --section integrations   # "claude-code" check

Path B — install as a Claude Code plugin

Ship a first-party Claude Code plugin under plugins/claude-code-opencontext/:

• .claude-plugin/plugin.json manifest referencing an MCP server definition for opencontext mcp
• Packaged skill(s): reuse the existing skill-body.md for the opencontext skill
• Slash commands mapped from the DSH surface: /oc doctor, /oc search, /oc remember

Additionally host a marketplace manifest at the repo root (.claude-plugin/marketplace.json) so installation becomes:

/plugin marketplace add melandlabs/opencontext
/plugin install opencontext@melandlabs

Once published to npm, claude plugin install should work directly too.

Acceptance criteria

• opencontext mcp install --target claude-code writes valid config for both project and user scopes and is idempotent
• A fresh Claude Code session lists the oc_* tools and can recall/write shared memory
• /oc doctor runs inside Claude Code and reflects the host environment (cwd, profile)
• Marketplace install path verified end-to-end

Alternatives considered

• Tell users to use claude mcp add manually (status quo): unmanaged, and it silently breaks when default providers change.
• MCP registry listing only: solves discovery but not the skill/command packaging we already provide for DSH.

Where does this change live?

New plugin workspace plugins/claude-code-opencontext/ plus an install subcommand / integration section in packages/opencontext/src/cli/ (shared logic with the Codex target).