feat: DecisionSearchService — search, filter, and ranking for decisions (#69)

[csharpfritz]

Summary

Closes #69 — Adds a pure service-layer DecisionSearchService that provides full-text search, date range filtering, and author filtering for parsed decisions.

Working as Linus (Backend Dev).

What's New

src/services/DecisionSearchService.ts

New stateless service operating on DecisionEntry[] arrays:

Method	Description
search(decisions, query)	Full-text search with relevance ranking
filterByDate(decisions, start, end)	Inclusive date range filter
filterByAuthor(decisions, author)	Case-insensitive substring match
filter(decisions, criteria)	Combined criteria — chains all three

Ranking strategy: title match (10×) > author match (5×) > content match (3×). Multi-word queries are split on whitespace; each term scored independently and summed.

Exported Types

• DecisionSearchCriteria — criteria bundle for the combined filter() method
• ScoredDecision — decision + relevance score pair

Tests

37 new tests in decisionSearchService.test.ts covering:

• Search: empty query, title/content/author matching, case-insensitivity, ranking, multi-word queries
• Date filtering: inclusive range, single-day, missing dates, empty range
• Author filtering: exact, partial, case-insensitive, missing authors
• Combined: all criteria together, partial criteria, open-ended date ranges
• Edge cases: regex characters in query, empty arrays, long queries, reversed date ranges

Design Decisions

• Decoupled from DecisionService — operates on DecisionEntry[], not files
• No VS Code deps — pure TypeScript, testable in isolation
• No model changes — DecisionEntry already had all needed fields
• Search-first chaining in filter() preserves relevance ordering through subsequent filters

For Rusty

The tree view integration is your follow-up. The filter() method accepts a DecisionSearchCriteria object — bind the search box and filter controls to this interface. Import from src/services:

import { DecisionSearchService, DecisionSearchCriteria } from '../services';

Test Results

All 1093 tests passing (1056 existing + 37 new).