feat(skills): import 17 skills from local-dev; fix stale host

Consolidating the divergence between this repo and local-dev's embedded
~/dev/.skills/ (the two had drifted; the 19 overlapping skills were byte-identical).

- Import the 17 skills that existed only in local-dev: discovery-framing,
  stage-gate-review, web-shot, and the 14 superpowers-* skills. This repo is now
  the superset / single source of truth.
- SKILLS_INDEX.md: add rows for the 17.
- install.sh + Taskfile.yml: git.d-ma.be host (was stale gitea.d-ma.be, which
  broke the one-line curl|bash installer post-rename).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Taskfile.yml

@@ -9,7 +9,7 @@ version: '3'
 # install.sh during the post-clone wire step.
 
 vars:
-  REPO_URL: 'https://gitea.d-ma.be/mathias/skills.git'
+  REPO_URL: 'https://git.d-ma.be/mathias/skills.git'
   CHECKOUT_DIR: '{{.HOME}}/.local/share/skills'
   CLAUDE_GLOBAL_DIR: '{{.HOME}}/.claude/skills'
   CRUSH_DIR: '{{.HOME}}/.config/crush/skills'