feat(paperclip): replace library with Paperclip plugin (v0.2.0)

[benfrank241]

Summary

• Replaces the `@vectorize-io/hindsight-paperclip` npm library with a proper Paperclip plugin
• Works with all adapter types (Claude, Codex, Cursor, HTTP, Process) via the event system — no code changes required by operators
• Install once: `pnpm paperclipai plugin install @vectorize-io/hindsight-paperclip`

What Changed

Before	After
npm library — developers manually call `recall()`/`retain()`	Paperclip plugin — hooks fire automatically
HTTP adapter agents only	All adapter types
Requires code changes per agent	Install once, covers all agents

Hooks

Trigger	Action
`agent.run.started`	Recalls relevant memories, caches in plugin state
`agent.run.finished`	Auto-retains agent output with `runId` as document ID
`hindsight_recall` tool	Mid-run memory query (returns cache or live recall)
`hindsight_retain` tool	Mid-run memory store
`onValidateConfig`	Live connectivity check on save

Test plan

• 15 unit tests passing (`npm test`)
• Build passes (`npm run build`)
• Manual: install plugin in a local Paperclip instance and verify recall/retain fire

Closes #918

[nicoloboschi]

LGTM