Add agent save/resume for automated working state

[coldlogicAI]

Closes #18.

Problem

Agents cannot persist and recover working state without a human in the loop. SessionStart offered a continuation once and told Claude not to load it until the user confirmed. Same-repo continuity was deferred to git and CLAUDE.md, so 3Notch was unused for automated agentic workflows.

Change

• notch save writes a continuation packet from the current Git snapshot plus optional --summary / --next-steps (stdin accepted). Secret scan still blocks. Packets are tagged continuation / stream-<stream> / source-save and supersede the latest same-stream checkpoint.
• notch resume prints the latest continuation for this store with no confirm prompt. Empty store is quiet success; --json returns "checkpoint": null. --include-private is required to resume private packets.
• Claude Code SessionStart injects the checkpoint body into additionalContext. It does not offer approve-then-get_packet as the happy path and still does not read transcript_path.
• MCP save_working_state and resume_working_state match the CLI. Private packets stay hidden unless the server starts with --include-private.
• AGENTS.md, README, continuation guide, and Codex/Grok/Cursor prompts: wrap-up is notch save; session start is notch resume. No daemon.

Migrations: none.

Testing

• npm run lint — pass
• npm run type-check — pass
• npm run build — pass
• npm test — 250 passed
• npm run test:e2e — 24 passed
• Built CLI smoke: node dist/cli/index.js --help lists save and resume

Review

Diff-scoped review: the change does what issue #18 claims (save, resume, SessionStart body injection, MCP parity, docs, tests). This is not a system review of packet integrity, inbox, or hook coverage beyond the files in this diff.

Not checked

• Visual / live Claude Code SessionStart against a real Claude Code process
• Existing stores whose allowedMcpWriteTools predates save_working_state (re-onboard or add the tool to config)
• Website publish of the continuation-checkpoints HTML mirror
• Cross-product behavior (iPSM, Derive)
• Whether prompt-mode still asking before creating a semantic checkpoint is the right long-term create policy (load path is automatic; create path is unchanged)

[coldlogicAI]

Cross-model review (Claude Sonnet, read-only): request-changes.

Addressed:

• onboard default README no longer says load waits for confirmation
• SessionStart does not inject private bodies unless continuation.sensitivity is private
• resume no longer silently falls back to another stream
• dead offeredCheckpointId write removed; re-inject on SessionStart kept (that is the agentic path)

Not checked by reviewer: they did not run the suite. Parent ran npm test (250), lint, type-check after the fixes.