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/error.rs

@@ -16,12 +16,16 @@ pub enum IdxError {
     ParseError(String),
     #[error("cache miss: {0}")]
     CacheMiss(String),
+    #[error("offline: {0}")]
+    Offline(String),
     #[error("config error: {0}")]
     ConfigError(String),
     #[error("io error: {0}")]
     Io(String),
     #[error("http error: {0}")]
     Http(String),
+    #[error("auth error: {0}")]
+    AuthError(String),
 }
 
 #[derive(Debug, Clone, Copy, Serialize, PartialEq, Eq)]
@@ -32,9 +36,11 @@ pub enum ErrorCode {
     Unsupported,
     ParseError,
     CacheMiss,
+    Offline,
     ConfigError,
     Io,
     Http,
+    AuthError,
 }
 
 impl IdxError {
@@ -46,9 +52,11 @@ impl IdxError {
             Self::Unsupported(_) => ErrorCode::Unsupported,
             Self::ParseError(_) => ErrorCode::ParseError,
             Self::CacheMiss(_) => ErrorCode::CacheMiss,
+            Self::Offline(_) => ErrorCode::Offline,
             Self::ConfigError(_) => ErrorCode::ConfigError,
             Self::Io(_) => ErrorCode::Io,
             Self::Http(_) => ErrorCode::Http,
+            Self::AuthError(_) => ErrorCode::AuthError,
         }
     }