feat(framework): P0 — MIT license + executable-leak sanitization

First phase of the framework constitution alpha. No behavior change for
configured installs.

- Add MIT LICENSE (root + framework bundle) + "license":"MIT" in manifests
- Drop private jarvis-brain credential fallback at 3 sites; default to
  $HOME/.config/mosaic/credentials.json (aligns with #551)
- prevent-memory-write.sh: soft-degrade OpenBrain nudge via ${OPENBRAIN_URL},
  removing hardcoded brain.woltje.com; still blocks the write

Refs #542, closes #569

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

packages/mosaic/framework/tools/git/detect-platform.sh

@@ -86,7 +86,7 @@ gitea_url_matches_host() {
 
 get_gitea_service_for_host() {
     local host="$1"
-    local cred_file="${MOSAIC_CREDENTIALS_FILE:-$HOME/src/jarvis-brain/credentials.json}"
+    local cred_file="${MOSAIC_CREDENTIALS_FILE:-$HOME/.config/mosaic/credentials.json}"
 
     case "$host" in
         git.mosaicstack.dev)