docs: add GitHub Copilot instructions

.github/copilot-instructions.md

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+# GitHub Copilot Instructions
+
+This is an electronic component inventory management system built with Phoenix LiveView. Follow these project-specific patterns for effective contributions.
+
+## Project Architecture
+
+**Core Structure**: Phoenix 1.8 with LiveView-first architecture for real-time inventory management
+- `lib/components_elixir/` - Business logic contexts (Inventory, AprilTag, Auth)
+- `lib/components_elixir_web/live/` - LiveView modules for real-time UI
+- Key contexts: `Inventory` (components/categories/locations), `DatasheetDownloader`, `AprilTag`
+
+**Hierarchical Data Pattern**: Both categories and storage locations use unlimited nesting
+```elixir
+# Use Hierarchical module for tree operations
+alias ComponentsElixir.Inventory.Hierarchical
+Hierarchical.build_tree(categories) # Converts flat list to nested structure
+```
+
+**Authentication**: Simple session-based auth using `ComponentsElixir.Auth`
+- All LiveViews must check `Auth.authenticated?(session)` in mount/3
+- Default password: "changeme" (configurable via `AUTH_PASSWORD` env var)
+
+## Key Development Workflows
+
+**Development Setup**:
+```bash
+mix deps.get
+mix ecto.setup  # Creates DB, runs migrations, seeds data
+mix phx.server  # Starts dev server with hot reload
+```
+
+**Code Quality (Critical)**: Always run before committing
+```bash
+mix precommit  # Compiles with warnings-as-errors, formats, runs tests
+```
+
+**Database Operations**:
+```bash
+mix ecto.reset           # Drop/recreate/migrate/seed database
+mix ecto.gen.migration   # Generate new migration
+```
+
+## LiveView Patterns
+
+**Stream-Based Components**: Use LiveView streams for component lists to prevent memory issues:
+```elixir
+# In LiveView
+stream(socket, :components, components)
+
+# In template
+<div id="components" phx-update="stream">
+  <div :for={{id, component} <- @streams.components} id={id}>
+    <!-- component content -->
+  </div>
+</div>
+```
+
+**File Upload Handling**: Uses Phoenix.LiveView.Upload with custom validators
+- Datasheets: PDF only, 10MB max, stored in `uploads/datasheets/`
+- Images: JPEG/PNG only, 5MB max, stored in `uploads/images/`
+
+## Database Conventions
+
+**Hierarchical Relationships**: Self-referential `parent_id` foreign keys
+```elixir
+# Schema pattern for categories/locations
+field :parent_id, :id
+belongs_to :parent, __MODULE__
+has_many :children, __MODULE__, foreign_key: :parent_id
+```
+
+**Component Search**: Full-text search across name, description, keywords
+```elixir
+# Use ilike for case-insensitive search
+from c in Component, where: ilike(c.name, ^"%#{search}%")
+```
+
+## Asset Management
+
+**DaisyUI Components**: Prefer DaisyUI classes for consistent styling:
+- `btn btn-primary` for buttons
+- `card card-compact` for component cards
+- `badge` for category/location tags
+
+## External Dependencies
+
+**AprilTag Generation**: SVG-based tags for physical location labeling
+```elixir
+ComponentsElixir.AprilTag.generate_svg(tag_id) # Returns SVG string
+```
+
+## Testing Guidelines
+
+**Factory Pattern**: Use explicit test data setup, not factories
+- Seed realistic test data in `test/support/` modules
+- Test both hierarchical and flat data structures
+
+## Production Deployment
+
+**Docker-First**: Primary deployment method via `docker-compose.yml`
+- Environment: `SECRET_KEY_BASE`, `AUTH_PASSWORD`, `PHX_HOST`
+- File uploads mounted as volumes: `./uploads:/app/uploads`
+
+**Release Commands**: Database migrations via release tasks
+```bash
+# In production container
+./bin/components_elixir eval "ComponentsElixir.Release.migrate"
+```
+
+## CI/CD with Gitea Actions
+
+**Gitea Actions Limitations** (important differences from GitHub Actions):
+- No `concurrency`, `run-name`, `permissions`, `timeout-minutes`, `continue-on-error` support
+- Limited expression support (only `always()` function)
+- No package repository authorization - use Personal Access Token for OCI publishing
+- Problem matchers and error annotations are ignored
+- Simple `runs-on` syntax only (`runs-on: ubuntu-latest`, not complex selectors)
+
+**CI Pipeline Will Include**:
+- Code quality checks (`mix precommit`)
+- Test execution across Elixir/OTP versions  
+- Docker image building and publishing (requires PAT for package registry)
+- Database migration testing
+
+Ensure all code passes `mix precommit` before pushing, as this will be enforced in CI.