feat: mdgrep 0.1.0 – boolean full-text search for Markdown

- query language: substrings, phrases, /regex/, AND/OR/NOT (+ UND/ODER/NICHT),
  parentheses; case-insensitive; ReDoS protection via regex timeouts;
  syntax errors with stable code and position
- SearchEngine over in-memory blocks: filters, predicate, grouping, sorting,
  paging, time budget, automatic reload, highlighted snippets
- Markdown loader with split modes file/heading/list/paragraph
- grep-like CLI (mdgrep), JSON output, grep exit codes
- Flask blueprint/app with JSON API and widget assets, dev server
- framework-free JS widget: live search, URL state, filters, paging,
  syntax help, en/de labels, CSS custom properties for theming

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

LICENSE

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+MIT License
+
+Copyright (c) 2026 Dieter Schlüter
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.