R4: Honest scope docs, CHANGELOG, and integration guides for stubbed surfaces

[jmcte]

Goal

Set correct expectations about what v0.1.0 ships and what is intentionally stubbed, so external users understand the scope without filing false bug reports against the live adapter or production exporter.

This is R4 of six release milestones (R1–R6) leading to v0.1.0.

Evidence

• src/mailplus_intelligence/live_adapter.py:80–85 — _fetch_messages is a stub returning [].
• src/mailplus_intelligence/exporters.py enforces dry_run=True and rejects live writes.
• pyproject.toml:7 — version 0.1.0 with no changelog or release-history file.
• README.md describes the long-term architecture but does not call out which pieces are stubbed in v0.1.

Acceptance criteria

Scope statement in README

• New "What's in v0.1" section in README.md immediately after the architecture overview, with two subsections:
  • Working end-to-end: fixture-mode sync, schema, threading, classification, suppression, deterministic extraction, LLM extraction (with [llm] extra), promotion queue, dry-run exporters, scheduler, CLI, doctor.
  • Stubbed / not-yet-wired: live MailPlus/IMAP adapter (returns empty batches), production export to wiki/memory//reminders (dry-run only).
• Each stubbed item links to its integration guide (below) and the issue tracking the live work.

Integration guides

• docs/integration/live-mailplus-adapter.md — what live_adapter.py expects, the env vars, the SyncBatch shape that _fetch_messages must return, and a worked example of a third-party stub talking to a generic IMAP server. Marked as "v0.2 territory; PRs welcome".
• docs/integration/live-export.md — what an exporter that promotes to wiki / memory/ / reminders needs to honor (provenance, rollback, idempotency), referencing docs/promotion-review-workflow.md. Marked as "v0.2 territory".

Changelog and versioning policy

• New CHANGELOG.md (Keep-a-Changelog format) with an ## [Unreleased] header and a populated ## [0.1.0] - YYYY-MM-DD section listing the closed M0–M5 milestones at a feature level (not commit level).
• New docs/versioning.md (or a section in CONTRIBUTING.md) stating the semver policy: 0.x means breaking changes within minor versions are allowed but documented.
• Single source of truth for the version: pyproject.toml, exposed via mailplus_intelligence.__version__ (sourced from importlib.metadata). README and quickstart reference it from there, not duplicated.

Cross-references

• README.md "Roadmap status" section updated to point at the release-v0.1 label and Phase 2 issue Phase 2 planning: entity graph, proactive recall, and relationship memory #75.
• AGENTS.md updated with a one-line note that R1–R6 issues drive the public release.

Out of scope

• Actually implementing the live adapter or live exporters (those are post-v0.1 epics). This issue only documents them.

Definition of done

• All boxes checked.
• A reader of the public README can answer "should I expect live MailPlus to work?" within 30 seconds (answer: not yet, here's the plan).