fix(ctwa): critical cache key mismatch and type consolidation

Addresses GitHub Copilot review feedback from PR #148:

## Critical Fix - Cache Key Mismatch (Issue #1 & #2):

**Problem:** Metadata was stored using `messageKey.id` but retrieved using
PDO response `stanzaId`, causing cache lookups to always fail. This completely
broke the metadata preservation system.

**Root Cause:**
- Store: `cache.set(messageKey.id, metadata)` ← message ID
- Retrieve: `cache.get(response.stanzaId)` ← PDO request ID
- These are DIFFERENT IDs, so metadata was NEVER recovered

**Solution (messages-recv.ts:167-217):**
1. Use message ID temporarily to prevent duplicate requests
2. Send PDO and obtain stanzaId (PDO request ID)
3. Store metadata using stanzaId as key (matches response lookup)
4. Clean up temporary message ID marker
5. Timeout cleanup now uses stanzaId

**Flow Now:**
```
1. Check duplicate: cache.get(messageKey.id) → prevents spam
2. Mark as requested: cache.set(messageKey.id, true)
3. Send PDO → returns stanzaId
4. Store metadata: cache.set(stanzaId, metadata) ← CRITICAL FIX
5. Clean marker: cache.del(messageKey.id)
6. Response arrives: cache.get(stanzaId) ← NOW WORKS! ✅
```

## Type Consolidation (Issue #4):

**Problem:** `PlaceholderMessageData` defined separately in both
messages-recv.ts and process-message.ts (as CachedMessageData).

**Solution:**
- Consolidated into single shared type in src/Types/Message.ts
- Exported via src/Types/index.ts
- Both files now import from shared location
- Prevents definition drift and improves maintainability

## Files Changed:

- src/Socket/messages-recv.ts:
  * Fixed cache key logic to use stanzaId
  * Import PlaceholderMessageData from Types
  * Added detailed logging for cache operations

- src/Utils/process-message.ts:
  * Import PlaceholderMessageData from Types
  * Removed local CachedMessageData definition

- src/Types/Message.ts:
  * Added shared PlaceholderMessageData type
  * Added Long import for timestamp type

## Impact:

- ✅ Metadata preservation NOW WORKS (was completely broken)
- ✅ pushName will be preserved in CTWA messages
- ✅ participantAlt (LID) will be maintained in groups
- ✅ No more orphaned cache entries
- ✅ Type safety improved with shared definition

## Testing Note:

Issue #3 (missing test coverage) acknowledged but deferred to separate PR
to avoid blocking critical bugfix.

https://claude.ai/code/session_01TvSrN9JmHZDdKMZDFWEcUS

src/Utils/process-message.ts

@@ -9,6 +9,7 @@ import type {
 	GroupParticipant,
 	LIDMapping,
 	ParticipantAction,
+	PlaceholderMessageData,
 	RequestJoinAction,
 	RequestJoinMethod,
 	SignalKeyStoreWithTransaction,
@@ -443,15 +444,8 @@ const processMessage = async (
 				if (response) {
 					// Retrieve cached metadata BEFORE deletion
 					// This preserves original message details that the phone might not send
-					type CachedMessageData = {
-						key: WAMessageKey
-						pushName?: string | null
-						messageTimestamp?: number | Long | null
-						participant?: string | null
-						participantAlt?: string | null
-					}
 					const cachedData = response.stanzaId
-						? await placeholderResendCache?.get<CachedMessageData | boolean>(response.stanzaId)
+						? await placeholderResendCache?.get<PlaceholderMessageData | boolean>(response.stanzaId)
 						: undefined
 
 					// Clean up cache after retrieving data