PDF: lay each day out along a rail with transport mode icons

[aquasolterra]

The itinerary in the PDF export now reads like the app's timeline. Each day is a rail with places as dots in the trip's accent and legs as their transport mode's icon in a disc. The mode's name stays in the text.

What changed

• Layout (trip_pdf.dart): each row draws its own piece of the rail, from a day's first node to its last. A decision's accent bar is drawn per row in the text column, so the rail runs past it unbroken.
• Which icon: the one this database gives the mode (transportModeIconsByKey, read by the export). That includes an icon chosen for a built-in, which a bundle does not carry. pdfTransportModeIcon falls back to the bundle's custom-mode icon, then to the built-in's own.
• Icon font: Flutter's Material Icons font is CFF (OTTO), and package:pdf parses TrueType only. It falls back to Latin-1 and throws on the code point. assets/fonts/build_pdf_icons.py therefore converts exactly the Icons.* that transport_mode.dart names out of the SDK's own font into MaterialIconsPdf.ttf (~8 KB). The font is CC BY 4.0; its attribution is registered on the license page.
• Left side bearing fix: both icon fonts wrote lsb = 0 into hmtx, while the outlines start at xMin > 0. A TrueType renderer puts the origin at xMin − lsb, so each glyph was drawn shifted left. This affected the app too. Measured in Flutter's engine (flutter_test, Linux), the horse, gondola, chairlift and T-bar icons sat 8–15% of their size left of center; after rebuilding TransportGlyphs.ttf they are exactly centered.

Testing

• New tests: every icon in kTransportModeIcons has a glyph in the font the PDF picks for it; lsb == xMin for both fonts (fails on the old TransportGlyphs.ttf); icon resolution order; transportModeIconsByKey; the icon font is embedded for a trip with a leg.
• flutter analyze clean, full suite passes (1634).
• Rendered a sample trip with places, several modes, a decision and a leg without a mode, then inspected the result.
• TripPdfFonts.load() loads both fonts through the real asset bundle.

To check on a device (CI APK)

• Export a trip with legs as PDF and look at the rail and icons.
• In the timeline, the horse, gondola, chairlift and T-bar icons sit centered in their disc. Measured only on Linux so far.

No new or changed strings, so nothing is missing from app_zh.arb. SECURITY.md is unaffected: no new host, permission or parsed foreign format.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 83.69565% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
lib/features/sharing/trip_pdf.dart	86.90%	11 Missing ⚠️
...eatures/trips/presentation/trip_detail_screen.dart	0.00%	4 Missing ⚠️

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