feat: add media upload pipeline with multipart support, blurhash generation, and R2 storage

- Add project_media table with image/video variants, ordering, and metadata
- Implement multipart upload handlers with 50MB limit
- Generate blurhash placeholders and resize images to thumb/medium/full variants
- Update ProjectCard to use media carousel instead of mock gradients
- Add MediaManager component for drag-drop upload and reordering

migrations/20260115031618_add_project_media.sql

@@ -0,0 +1,24 @@
+-- Project media table for carousel support
+-- Each project can have multiple images/videos with ordering
+
+CREATE TYPE media_type AS ENUM ('image', 'video');
+
+CREATE TABLE project_media (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    project_id UUID NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    display_order INT NOT NULL DEFAULT 0,
+    media_type media_type NOT NULL,
+    original_filename TEXT NOT NULL,
+    r2_base_path TEXT NOT NULL,
+    variants JSONB NOT NULL,
+    width INT,
+    height INT,
+    size_bytes BIGINT NOT NULL,
+    blurhash TEXT,
+    metadata JSONB,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    
+    UNIQUE (project_id, display_order)
+);
+
+CREATE INDEX idx_project_media_project_id ON project_media(project_id);