docs: add agent guide

agents.md

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+# Agent Guide
+
+This repository is a browser-first photo mapping prototype.
+
+## Goals
+
+- Import public Nextcloud shares through the local server proxy.
+- Read EXIF and GPS data client-side whenever possible.
+- Show photos on OpenStreetMap with map markers, thumbnails, and fullscreen preview.
+- Keep the timeline, map, and import flow visually and behaviorally consistent.
+
+## Stack
+
+- TypeScript + Node.js
+- Server entry: `src/index.ts`
+- HTTP and HTML rendering: `src/server/request-handler.ts`
+- Shared environment config: `src/shared/env.ts`
+- Docker is supported via `Dockerfile`
+
+## Current Structure
+
+- `src/domain/` for core data shapes and route logic
+- `src/features/` for feature-specific logic
+- `src/shared/` for reusable helpers
+- `src/server/` for request handling and HTML output
+
+## Working Rules
+
+- Keep all visible UI text in English.
+- Keep copy concise and professional.
+- Prefer client-side processing; do not store uploaded images on the server.
+- Preserve the Nextcloud public-share flow and local proxy behavior.
+- Keep the timeline zoomable and tied to the selected date range.
+- Keep the code style consistent with the existing TypeScript/DOM approach.
+
+## UI Rules
+
+- Use a restrained, modern palette.
+- Prefer square or minimally rounded surfaces.
+- Keep the map, import panel, photo list, and timeline visually aligned.
+- Maintain thumbnail previews in map markers and photo lists.
+
+## Change Process
+
+- Make small, focused changes.
+- Use conventional commit messages.
+- Verify the result with `git diff --check` when possible.
+- Update the README only when the user-facing setup or features change.
+
+## Deployment Notes
+
+- The app is designed to run in a container.
+- Default host: `0.0.0.0`
+- Default port: `3000`