refactor: schema-driven architecture, capability traits, hardened error paths

- Split parse.rs into raw_types.rs (serde structs) + map.rs (pure transforms) for MSN and Yahoo
- Replace Yahoo fundamentals dynamic HashMap with typed structs (SummaryDetail, DefaultKeyStatistics, etc.)
- Introduce capability-based provider traits: QuoteProvider, FundamentalsProvider, HistoryProvider
- Add future MSN capability traits: ProfileProvider, EarningsProvider, FinancialsProvider,
  SentimentProvider, InsightsProvider, NewsProvider (all dead_code until wired to CLI)
- Add shared domain types in src/api/types.rs (CompanyProfile, EarningsReport, FinancialStatements,
  SentimentData, InsightData, NewsItem)
- Harden error propagation: Yahoo cookie auth, MSN partial fundamentals, history symbol context,
  cache clear failures
- Strict config parsing: invalid IDX_OUTPUT returns ConfigError instead of silent fallback
- Cache schema version enforcement: version mismatch treated as cache miss
- Extract fetch_with_cache() helper in cli/stocks.rs
- Add MSN retry/backoff parity with Yahoo client
- Standardize Option<T> policy through parse/map layers
- All 56 tests passing, clippy clean

src/config.rs

@@ -92,8 +92,13 @@ impl IdxConfig {
         if let Ok(output) = std::env::var("IDX_OUTPUT") {
             cfg.output = if output.eq_ignore_ascii_case("json") {
                 OutputFormat::Json
-            } else {
+            } else if output.eq_ignore_ascii_case("table") {
                 OutputFormat::Table
+            } else {
+                return Err(IdxError::ConfigError(format!(
+                    "invalid IDX_OUTPUT value: '{}', expected 'json' or 'table'",
+                    output
+                )));
             };
         }
         if let Ok(no_color) = std::env::var("IDX_NO_COLOR") {