feat: Typst-based time report PDF generation

[madisvain]

Summary

• Replaces the frontend @react-pdf/renderer approach (from Added minimal Time Report pdf component #207) with Typst as a Tauri sidecar binary for PDF generation
• Adds a generate_time_report_pdf Tauri command that compiles a Typst template into a PDF with the time report data
• Bundles Montserrat fonts and the Typst template as Tauri resources

Why Typst?

• Better fit for a Rust/Tauri project — Typst is a Rust-based typesetting system, keeping PDF logic on the backend
• Configurable templates — Typst templates are plain text files that users or developers can customize without touching application code
• Extensible — this same approach can be expanded to invoice PDFs and other document types, with user-selectable templates
• Cleaner separation — the frontend only sends data, the backend handles all rendering

Architecture

1. Typst sidecar binary — bundled via tauri.conf.json externalBin (excluded from git, downloaded per-platform)
2. Template — src-tauri/resources/templates/time-report.typ reads JSON data via sys.inputs
3. Fonts — Montserrat font files bundled in src-tauri/resources/fonts/
4. Backend command — generate_time_report_pdf in commands.rs serializes data to temp JSON, invokes Typst, returns result
5. Frontend — Export button calls invoke("generate_time_report_pdf") with report data and file path from save dialog

Changes

• src-tauri/Cargo.toml — added tauri-plugin-shell
• src-tauri/tauri.conf.json — added externalBin, resources, shell-capability
• src-tauri/capabilities/shell.json — sidecar permissions
• src-tauri/src/lib.rs — registered shell plugin and command
• src-tauri/src/commands.rs — generate_time_report_pdf command
• src-tauri/resources/templates/time-report.typ — Typst template
• src-tauri/resources/fonts/ — Montserrat Regular, Medium, SemiBold
• src/routes/time-tracking/reports.tsx — uses invoke() instead of disabled button

Setup

Contributors need to download the Typst binary for their platform:

# Example for macOS ARM
curl -L https://github.com/typst/typst/releases/download/v0.14.2/typst-aarch64-apple-darwin.tar.xz | tar xJ
mv typst-aarch64-apple-darwin/typst src-tauri/binaries/typst-aarch64-apple-darwin

Test plan

• Download Typst binary for your platform into src-tauri/binaries/
• cargo check in src-tauri/ compiles successfully
• pnpm lint passes
• Run app, navigate to Time Tracking > Reports, click Export
• Verify PDF is generated with correct layout (title, date range, client, table)

Supersedes #207

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