feat(plugin): holistic import of on-disk Claude state into mem0

When a user installs mem0-plugin, mem0 starts empty even though Claude
Code has been quietly accumulating their CLAUDE.md instructions,
auto-memory, and subagent learnings on disk for months. The existing
hooks capture live state going forward but cannot backfill what already
exists.

This commit adds a one-shot importer that walks every Claude state
surface and backfills it into mem0:

- `mem0-plugin/scripts/import_claude_state.py` (new, ~575 lines):
  discovers CLAUDE.md hierarchy (+ @imports), .claude/rules,
  ~/.claude/projects/*/memory, and ~/.claude/agent-memory; chunks each
  file at markdown headings (H2 default, H3 for oversize sections,
  small-sibling merge, code-fence safe); tags chunks with metadata
  matching the existing mem0-mcp skill vocabulary (convention /
  user_preference / task_learning / anti_pattern / decision); POSTs
  sequentially to /v1/memories/ with infer=True (server-side dedup).
  Marker file at ~/.mem0/imports/claude-state.json tracks content-hash
  per chunk for idempotent re-runs and crash-resume safety.

  Flags: --dry-run, --reset, --no-infer, --source <type>.

- `mem0-plugin/scripts/on_session_start.sh`: adds a one-time nudge
  block after the existing bootstrap output. Emits the holistic-import
  prompt only when ~/.mem0/imports/claude-state.json doesn't exist
  and the SOURCE isn't "compact". Propagates to Cursor and Codex for
  free (shared bash entry point).

- README, CHANGELOG, plugin.json bumped to 0.2.0.

Patterned exactly on the existing on_pre_compact.py: stdlib only
(urllib, hashlib, pathlib, argparse), reuses _identity.resolve_user_id,
same logging setup, same ~/.mem0/ storage convention. Zero new packages,
zero new deps.

Smoke-tested locally: --help renders, missing MEM0_API_KEY exits 1
with helpful message, hook emits nudge when marker absent and stays
silent when marker present.

Research and design context: https://www.notion.so/Claude-State-Holistic-Import-Research-Findings-366f22c70c9081d7abdcc6b94a80e8d9

mem0-plugin/.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "mem0",
-  "version": "0.1.3",
+  "version": "0.2.0",
   "description": "Mem0 memory layer for AI applications. Add persistent memory, personalization, and semantic search to Claude workflows using the Mem0 Platform MCP server.",
   "author": {
     "name": "Mem0",