feat: Optimize Scopus backend queries with functional indexes (issue #60)

## Problem

Scopus backend was taking 37ms per cached query, 40x slower than other
cached backends (<1ms). This was caused by SQL queries using LOWER()
functions without corresponding functional indexes, forcing full table
scans of Scopus's 30k+ journal records.

## Root Cause

The `search_journals_by_name()` method uses `LOWER(normalized_name)` and
`LOWER(display_name)` for case-insensitive matching, but no functional
indexes existed on these expressions. SQLite could not use the regular
indexes on these columns when wrapped in LOWER(), resulting in:
- Full table scan of 30,272 Scopus journals
- 37ms query time vs <1ms for other backends

## Solution

Add functional indexes on `LOWER(normalized_name)` and `LOWER(display_name)`
to enable efficient case-insensitive lookups for large datasets.

## Changes

- Add `idx_journals_normalized_name_lower` functional index
- Add `idx_journals_display_name_lower` functional index

## Performance Impact

Scopus cached queries: 37ms → <2ms (20x+ faster)

Before:
  ✓ scopus: BackendStatus.FOUND [cached] (37.38ms)

After:
  ✓ scopus: BackendStatus.FOUND [cached] (1.64ms)

This brings Scopus performance in line with other cached backends:
- doaj: 0.81ms
- retraction_watch: 0.71ms
- scopus: 1.64ms ✓

## Testing

All 248 tests pass. Performance verified with multiple queries through CLI.

Resolves #60
Part of #52 - Performance: Optimize caching to eliminate redundant API calls

Author: florath

src/aletheia_probe/cache.py

@@ -154,6 +154,8 @@ def _init_database(self) -> None:
                 -- Indexes for performance
                 CREATE INDEX IF NOT EXISTS idx_journals_normalized_name ON journals(normalized_name);
                 CREATE INDEX IF NOT EXISTS idx_journals_display_name ON journals(display_name);
+                CREATE INDEX IF NOT EXISTS idx_journals_normalized_name_lower ON journals(LOWER(normalized_name));
+                CREATE INDEX IF NOT EXISTS idx_journals_display_name_lower ON journals(LOWER(display_name));
                 CREATE INDEX IF NOT EXISTS idx_journals_issn ON journals(issn);
                 CREATE INDEX IF NOT EXISTS idx_journals_eissn ON journals(eissn);
                 CREATE INDEX IF NOT EXISTS idx_journal_names_name ON journal_names(name);