fix: create sqlite db parent directory before opening

[NikiforovAll]

Problem

npx sideshow@0.8.0 serve crashes on first run:

Error: unable to open database file
    at createSqliteStorage (.../server/sqliteStorage.js)
  code: 'ERR_SQLITE_ERROR', errcode: 14, errstr: 'unable to open database file'

node:sqlite's DatabaseSync does not create missing parent directories. The default db path resolves to <package>/data/sideshow.db, but the package ships no data/ folder — so the directory never exists on a fresh install and every default-path startup fails. It reproduces regardless of port or working directory; the only workaround today is setting SIDESHOW_DB to a path whose directory already exists.

Proposal

In createSqliteStorage, mkdirSync(dirname(path), { recursive: true }) before opening the database, guarded by the existing path !== ":memory:" check so the in-memory contract suite is untouched.

Impact

• sideshow serve works out of the box on first run with no SIDESHOW_DB override.
• A user-supplied SIDESHOW_DB pointing into a not-yet-created directory now works too.
• No behavior change for :memory: or existing directories.

Verified: server boots against a nested non-existent db path and creates it; existing test/sqlStore.test.ts suite passes (30/30).