docs(readme): rewrite for story-first onboarding

Old README was reference-oriented — opened with abstract jargon
("reasoning chain memory") and led with manual CLI commands
before explaining the plugin flow. Average Claude Code user would
bounce in the first 10 seconds.

New structure:
- Opens with concrete pain point: "two weeks later, code remembers
  what, you don't remember why"
- Demo block shows the actual round-trip: prompt -> auto-recorded
  events -> pack output as Markdown the next time
- Plugin install leads (the typical path), manual setup demoted
  to its own section
- "How it works" in three plain bullets: auto-capture, artifacts,
  resume packs
- "Daily use" makes explicit that no manual commands are needed
- Manual CLI / MCP tools / config / event types stay as reference
  below

Also surfaces v0.5/v0.6 features that the old README missed
(goal/outcome, artifacts, async classifier, auto-open tasks) and
documents the TJ_CLASSIFIER_CLI / TJ_AUTO_OPEN_TASKS env vars.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: Shahinyanm