refactor: replace chromedp with browser native print for PDF export

Remove chromedp dependency, use window.print() instead. Docker image no longer needs Chromium (~200MB smaller).

- Delete services/pdf.go and templates/reports/review.html

- Remove PDF API route POST /api/repos/:id/review/pdf

- Add @media print CSS to review page

- Remove chromium from Dockerfile

CLAUDE.md

@@ -8,10 +8,10 @@ PR-Helper is a self-hosted web service that auto-generates PR descriptions from
 
 ## Tech Stack
 
-- **Backend**: Go + Gin + SQLite (go-sqlite3) + go-git + chromedp (PDF generation)
+- **Backend**: Go + Gin + SQLite (go-sqlite3) + go-git
 - **Frontend**: Go html/template + HTMX + D3.js + diff2html + Tailwind CSS
 - **LLM**: OpenAI-compatible API (SSE streaming)
-- **Deploy**: Docker (includes Chromium for PDF)
+- **Deploy**: Docker
 
 ## Build & Run
 
@@ -35,18 +35,17 @@ services/   → Business logic (git ops, LLM calls, PDF gen, cache management)
 models/     → Data models (repository, settings, analysis)
 database/   → SQLite init and migrations
 config/     → Configuration loading
-templates/  → Go HTML templates (layouts/, pages/, partials/, reports/)
+templates/  → Go HTML templates (layouts/, pages/, partials/)
 static/     → CSS (Tailwind output), JS (graph, diff-viewer, sse), vendor libs
 ```
 
-**Data flow**: Browser ↔ Gin handlers → services (git/llm/pdf) → SQLite + filesystem (`data/`)
+**Data flow**: Browser ↔ Gin handlers → services (git/llm) → SQLite + filesystem (`data/`)
 
 **Key service layer responsibilities**:
 - `services/git.go` — clone, diff, graph data extraction via go-git
 - `services/llm.go` — OpenAI-compatible API calls with SSE streaming
 - `services/generate.go` — PR description generation (commits + diff → LLM → structured output)
 - `services/review.go` — AI code review (per-file analysis + summary, Top-N strategy for large diffs)
-- `services/pdf.go` — chromedp HTML→PDF conversion
 - `services/cache.go` — repository cache lifecycle (clone, expiry cleanup)
 
 ## Key Patterns