fix: resolve TypeScript errors after SessionManager refactoring

- Remove unused import types (*SessionStatus, OpenAIMessage)
- Replace deprecated session functions with SessionManager API
- Prefix unused base class parameters with underscore
- Update all session management calls across agents and tools

Files affected:
- src/agents/*.ts (removed unused imports)
- src/utils/session-manager.ts (unused param prefixes)
- src/tools/server-tool.ts (SessionManager migration)
- src/tools/troubleshoot-tool.ts (SessionManager migration)
- src/routes/api/chat.ts (SessionManager migration)
- src/routes/handlers/message-handler.ts (SessionManager migration)

Verification:
- TypeScript: compiles without errors
- Tests: 223 passed (10 pre-existing failures)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/utils/session-manager.ts

@@ -123,7 +123,6 @@ export class SessionManager<T extends BaseSession> {
       // Build additional columns from subclass
       const additionalColumns = this.getAdditionalColumns(session);
       const additionalColumnNames = Object.keys(additionalColumns);
-      const additionalColumnPlaceholders = additionalColumnNames.map(() => '?').join(', ');
       const additionalColumnValues = Object.values(additionalColumns);
 
       // Build SQL with optional additional columns
@@ -277,10 +276,10 @@ export class SessionManager<T extends BaseSession> {
    * Override this method in subclasses to parse additional fields from DB result
    * (e.g., target_domain for DomainSession, last_recommendation for ServerSession)
    *
-   * @param result - Raw DB result
+   * @param _result - Raw DB result
    * @returns Additional fields to merge into session
    */
-  protected parseAdditionalFields(result: Record<string, unknown>): Partial<T> {
+  protected parseAdditionalFields(_result: Record<string, unknown>): Partial<T> {
     return {};
   }
 
@@ -288,10 +287,10 @@ export class SessionManager<T extends BaseSession> {
    * Override this method in subclasses to provide additional columns for saving
    * (e.g., target_domain for DomainSession, last_recommendation for ServerSession)
    *
-   * @param session - Session to save
+   * @param _session - Session to save
    * @returns Additional column values
    */
-  protected getAdditionalColumns(session: T): Record<string, unknown> {
+  protected getAdditionalColumns(_session: T): Record<string, unknown> {
     return {};
   }
 }