Add project philosophy document

Seven guiding principles: Privacy by Design, Data Ownership, Open Source,
Open Standards, AI-Assisted Development, Internationalization, Simplicity.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/philosophy.md

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+# Philosophy
+
+trails.cool is built on a set of principles that guide every decision — from
+architecture to product design to how we work.
+
+## Privacy by Design
+
+The Planner collects no personal data. Zero. Sessions are anonymous, there is
+no tracking, no analytics on user routes. This isn't just a feature — it's a
+commitment rooted in respect for the BRouter and bikerouter.de projects that
+inspire trails.cool.
+
+The Journal is equally mindful. All data we collect is documented in a
+user-visible **privacy manifest** that is always kept up to date. If it's not
+in the manifest, we don't collect it. Users should never be surprised by what
+we know about them.
+
+We don't sell data. We don't show ads. We don't build profiles.
+
+## Data Ownership
+
+Your routes and activities are yours. Not ours.
+
+- **Export everything**: Full export of all your data at any time, in open
+  formats (GPX, JSON). No lock-in, no "please contact support".
+- **Self-host**: Run your own Journal instance and own your data completely.
+  Migrate from trails.cool to your own server whenever you want.
+- **Documented formats**: Every data entity has clear, public documentation
+  of its format so you can build your own tools, visualizations, and
+  integrations around your data.
+- **Federation**: Your data lives on your instance. When you interact with
+  others across instances, your instance stays the canonical source.
+
+## Open Source
+
+trails.cool is MIT licensed. The entire codebase — Planner, Journal, shared
+packages, infrastructure — is open source.
+
+This is both a commitment to the open web and an acknowledgment of the
+projects that made trails.cool possible:
+
+- [BRouter](https://github.com/abrensch/brouter) — the routing engine
+- [bikerouter.de](https://bikerouter.de) — inspiration for the Planner
+- [brouter-web](https://github.com/nrenner/brouter-web) — the web client
+
+We benefit from open source. We contribute back to it.
+
+## Open Standards
+
+We build on open standards rather than inventing proprietary ones:
+
+- **GPX** for route and activity interchange
+- **ActivityPub** for federation between instances
+- **OpenStreetMap** for map data
+- **WebFinger** for identity discovery
+- **HTTP Signatures** for instance-to-instance trust
+
+When existing standards don't cover our needs, we extend them transparently
+(e.g., custom ActivityPub types for route collaboration) and document the
+extensions publicly.
+
+## AI-Assisted Development
+
+trails.cool is built with AI. Claude Code and OpenSpec are core tools in our
+development workflow. This is an experiment in how far spec-driven, AI-assisted
+development can take a real project.
+
+Human contributions are welcome and valued. AI is a tool, not a replacement
+for human judgment, design taste, or community input.
+
+The code is the code — regardless of who or what wrote it, it's held to the
+same standards of quality, security, and maintainability.
+
+## Internationalization
+
+trails.cool is international from day one. All user-facing strings go through
+react-i18next. We start with English and German, and welcome community
+contributions for additional languages.
+
+Trails don't have borders. Neither should the tools to explore them.
+
+## Simplicity
+
+We resist complexity. Every feature, every abstraction, every configuration
+option must earn its place.
+
+- Start with the simplest thing that works
+- Add complexity only when real users need it
+- One way to do things is better than two
+- If we can delete it and nobody notices, it shouldn't have been there
+
+This applies to architecture (single domain, simple permissions), to product
+(no feature creep), and to self-hosting (one Docker Compose file).