Build this tool: Bunker/Big-Build Series Thumbnail Consistency Checker
Product folder name: Build Series Thumbnail Checker

PRODUCT BRIEF
Tool where creator uploads thumbnails from a series, checks color palette/text placement consistency, flags outliers that break the visual pattern.

CONTEXT
Difficulty: Medium
Category: Howto & Style

TREND HOOK
Multi-day bunker digging series needs consistent thumbnail branding across many episodes.

VIDEO ANGLE
Short: "This bunker series thumbnails are all over the place — here's the fix." Long: build checker, run against a real multi-episode series' thumbnails.

WHY THIS TOOL
New take distinct from shipped Thumbnail Pattern Auditor (that's for stunt/adventure titles generally) — this is series-consistency specific.

STACK (standalone desktop app)
- Python 3 + tkinter GUI — standalone desktop tool (not a website).
- Even if the brief says "web app" / "site", ship a Python desktop GUI for v1.
- Include: main .py, requirements.txt, run_*.bat, build_exe.bat (PyInstaller), and an exports/ folder for saved output.
- Smoke-test core logic offline without requiring live API keys when possible.

GUI RULES
- Clean, readable dark or light UI — pick one consistent palette (no brand lock-in required).
- Clear app title / hero name derived from the product folder name.
- Short muted "How to use: …" line under the title (one sentence: what to enter → what button → what you get).
- Prefer real inputs (paste URL / fields / text) over fake demos.
- No sample dropdowns or canned demo datasets unless explicitly requested.
- Dropdowns: NEVER ttk.Combobox (unreadable on Windows dark UI). Use DarkSelect
  (preferred, no grab_set) OR dark-styled tk.OptionMenu (BG_ELEVATED / TEXT /
  active #243056 / BORDER+TEAL highlight; style the popup menu the same way).
  Never use grab_set (breaks close behavior on Windows).
- Handle window close with WM_DELETE_WINDOW.
- One job per tool; working copy/export; avoid overbuilt dashboards.

APIs & KEYS
- Never hardcode API keys or secrets into source or the packaged EXE.
- Store keys in a local user settings JSON under %LOCALAPPDATA%\<AppName>\ (or a single shared settings file if multiple tools share a key).
- Label each key field clearly in the UI (e.g. YouTube API key vs Gemini API key).
- Local/offline logic must work first; APIs are optional enhancements where possible.
- Call network APIs in a background thread; update the UI with after(...). On failure, keep local results and show a clear error.

YouTube Data API (v3)
- Add a shared YouTube Data API key field (these tools do not use OAuth).
- Use for: video/channel/playlist lookups, titles, descriptions, tags, statistics, search as needed by the brief.
- Prefer paste-a-URL / channel-ID inputs; parse video IDs from common YouTube URL formats.
- If captions/transcripts are needed, use the captions endpoint or a documented fallback (manual paste) when captions are disabled.
- Respect quotas; cache responses during a session when useful.

Gemini / LLM
- Not required for v1 (this is primarily an audit / organize / calculate tool).
- Skip LLM unless a later version needs generated copy.

IMPLEMENTATION NOTES
- Match the product brief closely; keep v1 focused on one job.
- Support Copy and/or Export of results where useful (TXT/CSV/JSON as fits the tool).
- Validate inputs; show empty/error states clearly.
- If scoring/grading: show score + short explanation of what failed/passed.
- If generating copy: show multiple variants when the brief asks for them.

OUTPUT
- Runnable standalone Python app
- requirements.txt + run bat + optional EXE build script
- In-app how-to line
- Example of typical input → output (in README or comments, not fake UI samples)