Add granular logging across all source files

Introduce logger infrastructure and add structured logging to every layer:
alpaca.ts (buy/sell/quote/clock), momentum-indicator.ts (evaluate flow),
momentum-strategy.ts (poll loop), index.ts (startup/cycle), and trading.ts
(market timing). Replace raw console.log calls with leveled logger. Update
all tests with appropriate console spies.

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

vitest.config.ts

@@ -4,5 +4,6 @@ export default defineConfig({
     test: {
         globals: true,
         exclude: ['dist/**', 'node_modules/**'],
+        env: { LOG_LEVEL: 'debug' },
     },
 });