hookify: not_contains operator does literal substring match, not regex — breaks the shipped require-tests-stop example

### Summary

The `require-tests-stop.local.md` example shipped in `plugins/hookify/examples/` (reproduced in the README under "Example 3: Require Tests Before Stopping") can never pass. The Stop hook it defines blocks unconditionally, regardless of whether tests were actually run.

### Repro

The example rule:

```yaml
operator: not_contains
pattern: npm test|pytest|cargo test
```

Enable it, then trigger a Stop event with a transcript that *does* contain a passing test run (e.g. `"npm test ran and passed"`). Expected: hook allows exit. Actual: hook still blocks.

### Root cause

`core/rule_engine.py`, in the operator dispatch (~line 168-173):

```python
elif operator == 'contains':
return pattern in field_value
elif operator == 'equals':
return pattern == field_value
elif operator == 'not_contains':
return pattern not in field_value
```

Only `regex_match` compiles `pattern` as a regex. `contains`/`not_contains`/`equals` treat `pattern` as a literal string. The example's `pattern: npm test|pytest|cargo test` is written expecting regex alternation (match any of the three), but under `not_contains` it's checked as one literal 26-character string — including the pipe characters — which will essentially never appear verbatim in a real transcript. So `not_contains` evaluates `True` unconditionally, and the rule blocks every Stop event.

### Impact

Anyone who enables this documented example gets a gate that looks like enforcement but isn't — arguably worse than no gate, since it gives false confidence that tests are being required.

### Verified

Reproduced by executing `hooks/stop.py` directly against synthetic transcripts (not just read from source): blocks with no test evidence (correct), still incorrectly blocks with `"npm test ran and passed"` or `"pytest"` present in the transcript.

### Fix

Since `_rule_matches` requires ALL conditions in a rule to match (AND semantics, `rule_engine.py:120-125`), and the README already documents this exact multi-condition pattern elsewhere ("Multiple Conditions" section), the example can be fixed with no code change — replace the single condition with three `not_contains` conditions ANDed together (De Morgan's law: `NOT(A or B or C)` = `NOT A AND NOT B AND NOT C`):

```yaml
conditions:
- field: transcript
operator: not_contains
pattern: npm test
- field: transcript
operator: not_contains
pattern: pytest
- field: transcript
operator: not_contains
pattern: cargo test
```

I have this fix verified and staged (branch `fix/hookify-require-tests-not-contains-alternation` on my fork), but this repo's automation closes PRs from non-Anthropic-team-members on sight, so filing as an issue instead in case a maintainer wants to pick it up or point me at the right contribution path.

### Minor, unrelated

`plugins/hookify/.claude-plugin/plugin.json` has no `version` field, unlike sibling plugins in the marketplace.

Compare plugins/hookify/examples/require-tests-stop.local.md with the README's “Example 3: Require Tests Before Stopping,” then inspect hooks/stop.py and core/rule_engine.py. Run hooks/stop.py with synthetic transcripts containing no test evidence and each listed test command. Done means the example blocks without evidence, allows a transcript containing any one of the listed commands, and the example and README agree.

Written by the indexing model from the issue text.