Add install.sh / run.sh / bundled icon; fully pin requirements

- install.sh: one-time Linux Mint setup (apt, .venv, requirements, .desktop
  entry with absolute paths). Re-runnable.
- run.sh: launches the app from .venv (called by the menu entry).
- icon.png: bundled 256px red-cross launcher/window icon; app prefers it over
  the runtime-drawn fallback (data/icon.png).
- requirements.txt: fully pinned incl. transitive deps, tested on Python 3.12;
  numpy held at 2.2.6 so it installs on Python 3.10 too.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/README.md

@@ -16,7 +16,7 @@ code) and plots them on an interactive map.
 | [overview.md](overview.md) | What the app does, feature by feature |
 | [architecture.md](architecture.md) | Code structure, threading model, data flow |
 | [data-model.md](data-model.md) | The `orte.csv` schema and how it is read/written |
-| [setup.md](setup.md) | Install & run on a fresh Linux Mint machine, plus a desktop launcher |
+| [setup.md](setup.md) | `git clone` + `./install.sh` on Linux Mint; how updates work |
 | [improvements.md](improvements.md) | Prioritized review findings and suggested changes |
 | [changelog.md](changelog.md) | What has changed, newest first |
 | [dev-notes.md](dev-notes.md) | Assumptions that turned out wrong — read before editing |