feat: implement rich logging, progress percentages, and quota handling for Gmail sync

[HyperVon]

Overview

This Pull Request implements rich progress feedback, percentage indicators, and resilient rate-limit handling for the Gmail active sync pipeline on both the backend and frontend.

Problem

Previously, triggering a manual Gmail sync was silent in the logs and showed static/uninformative status states (e.g. just a generic "Syncing...") in the UI. In addition:

1. Long-running syncs (with hundreds of emails) could exceed the Gemini API daily free tier quota (20 requests per day), causing the backend to continuously throw 429 exceptions and freeze in a stuck state.
2. A race condition existed where the backend would spawn the async task, but the frontend's immediate subsequent dashboard reload occurred before the database claimed the lock, requiring a manual refresh to see the active status.

Changes Made

1. Backend Service & Lock Management

• Synchronous Sync Handshake: Refactored initiateManualSync in GmailIntegrationService.java to claim the lock and initialize the status synchronously on the HTTP thread, fully resolving the dashboard reload race condition.
• Background Runner: Offloaded the heavy lifting (scanning, message downloading, and AI extraction) to the askExecutor asynchronously.
• Startup Lock Clean: Created a StartupInitializer (CommandLineRunner) to automatically clear any stale database locks and sync statuses upon server boot.

2. Granular Progress & Quota Resilience

• Step Counts & Percentages: Added real-time progress calculations for the email detail download stage (Downloading details (X/Y - P%)...) and the Gemini extraction stage (Extracting jobs with Gemini AI (batch X/Y - P%)...).
• Cache Eviction: Added active cache eviction inside the sync status updates so that the frontend's dashboard queries bypass Spring's @Cacheable boundaries to fetch the live state.
• Graceful Gemini Quota Failover: Monitored HttpClientErrorException (status 429) from Google AI Studio. Upon quota exhaustion, the sync gracefully terminates early, releases the lock, and displays a permanent user message: Sync paused: Gemini API daily quota exceeded. Please try again tomorrow.

3. Frontend UI & State Enhancements

• Dynamic Polling Acceleration: Programmed a reactive effect in job.service.ts to temporarily accelerate polling to 2 seconds during active sync, reverting to 30 seconds on completion.
• Type-safe UI Indicator: Leveraged Angular's control-flow @if (syncStatus(); as status) to narrow type-checking. Displayed solid, static status text next to the Sync button for legibility, with dynamic warning styling (in red) for error states.