Implement search_notes from its specification

search_notes in src/notesapi/search.py is declared, documented and tested,

but its body raises NotImplementedError. Write it.

The full contract — matching, ranking, filtering and paging, in the order the

rules are applied — is in the module's docstring. Read it before writing a line

of code; it is the specification, and the evaluation measures against it.

The short version

• A query is whitespace-separated terms; a note matches when every term

occurs (case-insensitively, as a substring) in its body or a tag.

• An empty or blank query matches every live note.
• Score: one point per term found in the body, two per term found in a tag.
• Order: score descending, then updated_at descending, then note_id

ascending.

• Deleted notes never match. With tags, a note must carry every one of them

(case-insensitively) to be considered. offset skips, limit caps

(None = no cap); a negative offset or limit raises ValueError.

• Return the notes, not their ids. Never modify the store.

Boundaries

• Implement it in src/notesapi/search.py; the public API of notesapi stays

as it is.

• Do not modify the repository test suite under tests/ and do not add

third-party dependencies — the standard library is enough.

• The repository's own test suite (pytest) has to stay green, so the

store, errors, sync modules and their behaviour must keep working.