Tighten PR template and CONTRIBUTING to gate visual/style changes

The post-launch PR flood from LLM coding agents drowned the repo in PRs
that don't run the app, attach no screenshots, and invent parallel
component styling. Even tiny correctness fixes accumulated into a visual
mess. Make the rules explicit in both the PR template and CONTRIBUTING:

- Run the app and view the change in a browser before submitting.
- Required screenshot for any UI/render touch (no longer "delete if not UI").
- Explicit style requirements: reuse CSS variables, no Unicode emoji
  (use SVG icons), monospaced font, dark theme, no parallel widgets.
- Direct callout for bulk agent-generated PRs: open an issue first.

PRs that ignore these will be closed without merge, regardless of code
correctness.

.github/pull_request_template.md

@@ -23,6 +23,7 @@ Fixes #
 - [ ] I searched [open issues](https://github.com/pewdiepie-archdaemon/odysseus/issues) and [open PRs](https://github.com/pewdiepie-archdaemon/odysseus/pulls) — this is not a duplicate.
 - [ ] This PR targets `main`
 - [ ] My changes are limited to the scope described above — no unrelated refactors or whitespace changes mixed in.
+- [ ] I actually ran the app (`docker compose up` or `uvicorn app:app`) and verified the change works end-to-end. Type-checks and unit tests are not enough.
 
 ## How to Test
 
@@ -33,6 +34,20 @@ Fixes #
 2.
 3.
 
-## Screenshots (UI changes only)
+## Visual / UI changes — REQUIRED if you touched anything that renders
 
-<!-- Drag and drop images or a screen recording here. Delete this section if not a UI change. -->
+**Anything that changes what the UI looks like — buttons, icons, padding, colors, fonts, spacing, layout, CSS, HTML, SVG, or any `static/js/` module that draws to the DOM — needs all of the following. PRs that change rendering without these WILL be closed.**
+
+- [ ] **Screenshot or short clip** of the change in the running app, attached below. Mobile screenshot too if the change affects mobile.
+- [ ] **Style match**: the change uses Odysseus's existing visual language. Specifically:
+  - Reuse existing CSS variables (`--red`, `--fg`, `--bg`, `--card`, `--border`, etc.) — do not introduce new color values, font sizes, or spacing units.
+  - Reuse existing button/input/card/border classes. Don't invent parallel styling.
+  - **No Unicode emoji in UI or code.** Use inline SVG (matching the monochrome icon style already in `static/index.html`) or plain text.
+  - Monospaced font (`Fira Code`) for primary UI text. Don't override.
+  - Dark theme is the default; any light-mode work must be wired through the existing theme system, not hard-coded.
+- [ ] **No new component patterns.** If a similar widget already exists in the app, extend it instead of writing a parallel one.
+- [ ] **I am not an LLM agent submitting a bulk PR.** If you are, please open an issue describing the problem first — bulk auto-generated PRs that don't match the project's visual style are closed on sight, even when the underlying fix is correct.
+
+### Screenshots / clips
+
+<!-- Drag and drop images or a screen recording here. Required for any UI/visual change. -->