feat!: optional fail-closed fallback, legend output, richer prompt & docs

BREAKING CHANGE: regex fallback is now opt-in (patterns no longer defaults
to presets.swiss). With no fallback an LLM failure throws AnonymizationError
(fail-closed) and the pre-filter is bypassed; at least one of llm/patterns is
required. AnonymizationResult gains a required `legend`; anonymizeChunks seed
is now { mapping, legend? } and returns legend.

- prompt: model may coin new UPPERCASE abbreviations and returns a 'legende'
  explaining every abbreviation used (French); backfilled by DEFAULT_LEGEND
- PatternDef.meaning surfaces in the legend; swiss/generic presets get meanings
- AnonymizationError (exported) wraps the cause on fail-closed
- README: drop the chatbot provenance line; add 'How it works' + nLPD sections
- 34 tests / 99% coverage; bump to 0.2.0

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@mobiletic/anonymizer",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "description": "Framework-agnostic PII anonymization & pseudonymization: pluggable LLM detection for free-form PII (names, addresses) with a deterministic regex fallback, deterministic coreference, and streaming-safe de-anonymization.",
   "license": "MIT",
   "author": "Mobiletic",