chore: planning gate — milestones, issues, and task breakdown

Break PRD into 8 milestones (Phase 0–7) with 59 issues on Gitea.
Populate TASKS.md, update mission manifest, initialize scratchpad.
Repo created at git.mosaicstack.dev/mosaic/mosaic-stack.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.mosaic/quality-rails.yml

@@ -0,0 +1,10 @@
+enabled: false
+template: ""
+
+# Set enabled: true and choose one template:
+# - typescript-node
+# - typescript-nextjs
+# - monorepo
+#
+# Apply manually:
+#   ~/.mosaic/bin/mosaic-quality-apply --template <template> --target <repo>