docs: Forgejo branding deploy notes (exchange-dark)

Document live paths, DEFAULT_THEME vs user.theme, and safe asset deploy
without touching data/git repositories.

2026/2026-07-10--forgejo-theme-exchange-dark.md

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+# 2026-07-10 — Forgejo global theme (exchange-dark)
+
+## Goal
+
+Make https://git.hacktivism.ch look closer to https://exchange.hacktivism.ch: warm dark layout, gold + teal accents, readable text.
+
+## Done on koopa
+
+- Custom theme file `theme-hacktivism.css` (full variable set from forgejo-dark + exchange palette).
+- Installed under `~/koopa-forgejo/data/custom/public/assets/css/` (and gitea/custom mirror).
+- Logo/favicon under `…/assets/img/`.
+- `DEFAULT_THEME = hacktivism` in app.ini + compose `FORGEJO__ui__*`.
+- Forced DB: `UPDATE "user" SET theme = 'hacktivism'` (logged-in preference was still `forgejo-auto`).
+
+## Readability
+
+- Body/text cream on `#1a1410`; muted secondary not below ~`#c9b8a0`.
+- Gold primary buttons with dark label text.
+- Explicit overrides for menus, forms, code, labels, messages, footer.
+
+## Admin-log
+
+Source of truth: `configs/forgejo/assets/` + `configs/forgejo/README.md`.
+
+## Note
+
+Browser cache may hold old CSS (`Cache-Control: max-age=21600`). Hard-reload or private window if UI looks stale.