sciagent code + Gitea Actions CI/CD

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

be0/migrations/018_imagehub_segmentation_links.sql

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+-- ImageHub: link organ-segmentation masks to their parent image file (Phase D).
+-- A mask file (file_kind='segmentation') points at the image it segments via a
+-- self-referential parent_file_id (e.g. an organ mask of ct.nii.gz); organ_label
+-- names the organ. Regular files stay file_kind='image'. Idempotent (ADD COLUMN IF
+-- NOT EXISTS) so the startup runner can apply it to volumes that predate it.
+-- Apply after 017_imagehub_datasets.sql (no semicolons inside comments — the runner
+-- splitter is naive):
+--   docker exec -i initiative-postgres psql -U initiative -d initiatives < be0/migrations/018_imagehub_segmentation_links.sql
+
+ALTER TABLE imagehub_dataset_files
+  ADD COLUMN IF NOT EXISTS file_kind TEXT NOT NULL DEFAULT 'image' CHECK (file_kind IN ('image','segmentation'));
+
+ALTER TABLE imagehub_dataset_files
+  ADD COLUMN IF NOT EXISTS parent_file_id UUID REFERENCES imagehub_dataset_files(id) ON DELETE CASCADE;
+
+ALTER TABLE imagehub_dataset_files
+  ADD COLUMN IF NOT EXISTS organ_label TEXT NOT NULL DEFAULT '';
+
+-- List all masks of an image efficiently.
+CREATE INDEX IF NOT EXISTS idx_imagehub_dataset_files_parent
+  ON imagehub_dataset_files (parent_file_id);