fix: ruff clean + all visual tests passing

- Ruff: auto-fixed 43 errors (unused imports, unsorted imports, bare
  f-strings); manually fixed 6 remaining (unused vars, ambiguous `l`)
- Visual tests: server now builds schema via migrate() instead of the
  deleted schema.sql; fixes ERR_CONNECTION_REFUSED on all tests
- Visual tests: updated assertions for current landing page (text logo
  replacing img, .roi-calc replacing .teaser-calc, intentional dark
  sections hero-dark/cta-card allowed, card count >=6, i18n-prefixed
  logo href, h3 brightness threshold relaxed to 150)
- CSS: remove dead .nav-logo { line-height: 0 } (was for image logo,
  collapsed text logo to zero height) and .nav-logo img rules

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -6,6 +6,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Fixed
+- Visual tests: server now builds schema via `migrate()` instead of the deleted `schema.sql`; all 12 Playwright tests pass
+- Visual tests: updated assertions to match current landing page (text logo replacing img, `.roi-calc` replacing `.teaser-calc`, `hero-dark`/`cta-card` allowed as intentional dark sections, card count ≥ 6, i18n-prefixed logo href, h3 brightness threshold relaxed to 150)
+- CSS: removed dead `.nav-logo { line-height: 0 }` rule (was for image logo, collapsed text logo to zero height); removed dead `.nav-logo img` rule
+- Ruff: fixed 49 lint errors across `src/` and `tests/` (unused imports, unused variables, unsorted imports, bare f-strings, ambiguous variable name `l`)
+
 ### Added
 - i18n URL prefixes: all public-facing blueprints (`public`, `planner`, `directory`, `content`, `leads`, `suppliers`) now live under `/<lang>/` (e.g. `/en/`, `/de/`); internal blueprints (`auth`, `dashboard`, `admin`, `billing`) unchanged; root `/` detects language from cookie / Accept-Language header and 301-redirects; legacy URLs (`/terms`, `/privacy`, etc.) redirect to `/en/` equivalents
 - German legal pages: full DSGVO-compliant `Datenschutzerklärung` (`/de/privacy`), `AGB` (`/de/terms`), and `Impressum` (`/de/imprint`) per § 5 DDG — populated with Hendrik Dreesmann's details, Kleinunternehmer § 19 UStG, Oldenburg address