feat: ph shell-hook + harness guard + docs restructure (v0.2.1)

[weijt606]

What's New

ph shell-hook — zero-config auto-wrap (3 new commands)

Installs a shell preexec hook that automatically intercepts claude/claw/codex/opencode commands and transparently routes them through ph wrap --auto-evolve — no manual prefix needed.

ph shell-hook install      # one-time setup, writes to ~/.zshrc
ph shell-hook status       # check installation state
ph shell-hook uninstall    # clean removal

Harness existence guard

The orchestrator now checks whether the Proposer actually generated harness.py before evaluation. Gives a clear error instead of a cryptic FileNotFoundError.

Documentation restructure

• Batch search loop diagram moved to Step 4; auto-evolution flow diagram moved to Step 6
• "How It Works" section simplified to text explanation with cross-references
• Full shell-hook usage documentation added to both READMEs

Changes

• cli.py — +147 lines: shell-hook command group (install/uninstall/status, hook script, helpers)
• orchestrator.py — +6 lines: harness.py existence guard
• test_evolution.py — +79 lines: 8 new tests (TestShellHook class)
• README.md / README_CN.md — diagram relocation + shell-hook docs
• CHANGELOG.md — v0.2.1 entry
• Version bump: 0.2.0 → 0.2.1

Validation

• 173 tests passed, ruff clean
• Manual smoke test: shell-hook install/status/uninstall, wrap, traces