add PDD workflow: CLAUDE.md, PDD.md, sprint spec with active symlink

docs/specs/sprint-001-sync-reliability.md

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+# Sprint 001 — Sync Reliability & Telegram Delivery
+
+**Dates:** Active
+
+## Goals
+
+- Fix daily sync on NAS
+- Verify Telegram delivery pipeline
+- Stabilize subscription fetching behind GFW
+
+## Tasks
+
+### T1: Fix daily sync cron
+
+**Description:**
+`t-youtube-daily-sync` errored last run. Determine if `run_sync.py` is the active pipeline or if VPS-based `fetch_and_sync.sh` replaced it. Fix whichever is active.
+
+**ACs:**
+- [ ] Daily sync completes without errors
+- [ ] New videos appear in dashboard
+
+**Impl Notes:**
+Check NAS cron logs. VPS sync fires every 6h.
+
+### T2: Verify tg-group-filter delivery
+
+**Description:**
+Cron switched from `deliver: local` to `deliver: all`. Confirm Telegram delivery works for filtered results.
+
+**ACs:**
+- [ ] Telegram receives filtered video digest
+- [ ] No duplicate deliveries