Add conflict resolution diff UI and app branding

.project/adrs/adr-003-ssr-strategy.md

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+# ADR-003: SSR Strategy - Go Templates with Preact Hydration
+
+## Status
+Accepted
+
+## Context
+The application needs to serve document pages that are readable without JavaScript (for performance and accessibility), while providing rich interactivity (comments, editing, search) when JavaScript is available. We need a server-side rendering strategy that works with our Go backend and Preact frontend.
+
+## Decision
+**Strategy C**: Go's `html/template` renders initial HTML for all pages. Preact hydrates interactive components on the client.
+
+### Implementation Details
+
+1. **Server Rendering**:
+   - Go handlers query database for document content
+   - Markdown parsed to HTML server-side (Goldmark)
+   - `html/template` renders full page with document HTML embedded
+   - No JavaScript required for reading
+
+2. **Client Hydration**:
+   - Preact components mount into designated DOM containers
+   - Comments, search, editor are Preact islands
+   - Static content remains server-rendered HTML
+   - `preact-iso` handles client-side navigation between pages
+
+3. **Data Passing**:
+   - Initial state embedded as JSON in `<script type="application/json">` tags
+   - Preact reads initial state during hydration, avoids extra API calls
+   - CSP nonce applied to all inline scripts
+
+## Consequences
+
+### Positive
+- First contentful paint is instant (pure HTML)
+- SEO-friendly without extra complexity
+- Graceful degradation: works without JS
+- Go templates are auto-escaping XSS-safe
+- No V8/JS runtime embedded in Go binary
+- Smaller client bundle (only interactive components)
+
+### Negative
+- Some code duplication: markdown parsing logic in both Go and JS (for preview)
+- Template syntax is verbose compared to JSX
+- Hydration can cause flicker if not carefully managed
+- Client state must reconcile with server-rendered HTML
+
+## Alternatives Considered
+
+### Go Templates Only (No Preact)
+- **Pros**: Zero client JS, maximum performance
+- **Cons**: No interactive features (comments, real-time sync, search)
+- **Rejected**: Doesn't meet collaboration requirements
+
+### Embedded JS Runtime (QuickJS/V8)
+- **Pros**: True isomorphic rendering, JSX templates
+- **Cons**: Adds C dependency, complex build, larger binary, security surface area
+- **Rejected**: Violates minimal dependency principle
+
+### Preact SSR via WASM
+- **Pros**: Same templates on server and client
+- **Cons**: WASM overhead, complex build pipeline, slower than Go templates
+- **Rejected**: Go templates are faster and simpler
+
+## References
+- Go html/template security: https://pkg.go.dev/html/template
+- Preact hydration: https://preactjs.com/guide/v10/server-side-rendering
+- Islands Architecture: https://jasonformat.com/islands-architecture/