[FEAT] PDF output for mooring reports (report --pdf) + print-layout fixes

[eleanorfrajka]

Summary

Wires up single-file PDF output for mooring reports and fixes the print layout so the merged PDF is usable on A4. The per-page HTML reports remain the single source of truth; the PDF is a post-processing step (WeasyPrint) that renders the existing pages, applies a print stylesheet, and concatenates them — report generation and the Jinja templates are unchanged except for one genuine consistency bug fixed along the way.

The combine logic (oceanarray/report/_pdf.py, combine_mooring_pdf) existed from an earlier session but was unreachable: not exported, not in the CLI, no install path for its dependency. This PR closes those gaps and then makes the rendered output actually fit the page.

PDF wiring

• New CLI flag oceanarray report MOORING --pdf — combines the generated HTML pages into {mooring}_report.pdf (reading order summary → per-instrument → stack → grid; only pages that exist are included). --all also builds the PDF.
• New optional extra pdf — pip install oceanarray[pdf] installs WeasyPrint (kept out of core because it pulls in native libs: pango, cairo, gdk-pixbuf).
• combine_mooring_pdf exported from oceanarray.report.
• Output directory is resolved through a single shared helper paths.resolve_report_dir (--output-dir → --report-dir/{mooring} → proc/{mooring}/report/), called by both the CLI PDF path and MooringReport.generate() so the PDF always reads exactly where the HTML was written (no drift).
• --array + --pdf warns that PDF isn't supported in array mode (the array index is HTML-only) rather than silently ignoring the flag.

Print-layout fixes (all in _pdf._PRINT_CSS unless noted)

These correct WeasyPrint-vs-browser divergences without changing the on-screen HTML:

• Figure widths — the templates already cap figures via the .fig convention (inline max-width:50%/33%/300px, etc.). An earlier img { max-width:100% !important } in the print CSS was overriding all of them and blowing every plot up to full page; removed the !important (kept a non-important max-width:100% overflow ceiling) so the per-figure caps win again.
• Metadata header — .meta-grid uses repeat(auto-fill, minmax(...)), which WeasyPrint collapses to one column; forced a fixed 3-column layout in print.
• Status pills (§2 pipeline) — shrunk .badge/.arrow and set the pipeline flex-wrap: nowrap so each instrument's status fits on one line.
• Copy-yaml boxes (§3.5) — <textarea rows="2"> rendered too short and clipped the second line; forced enough height.
• Tables — denser type + tighter padding in print; wide <th> allowed to wrap; body-text measure capped (~78ch) so explanatory notes don't run the full page width.
• Sensor-calibration font (§5, template fix in _mooring.py) — removed a stray inline font-size on the Model cell so it matches the rest of the table (fixes both screen and PDF).

Housekeeping

• .gitignore: ignore generated report output under tests/fixtures/proc/*/report/ (multi-MB HTML + PDFs) so it never enters history.

Tests

• tests/unit/test_pdf_report.py: reading-order resolution; empty-dir FileNotFoundError; PDF render (valid %PDF-); custom output path; real Jinja summary rendered to PDF; and the cmd_report --pdf CLI path end-to-end + --dry-run. Render tests gated on importorskip("weasyprint").
• tests/unit/test_cli.py: --pdf parser assertions.

Docs

reports.rst (new "PDF output" section), cli_reference.rst (--pdf flag), project_structure.md (_pdf.py).

Exit-code behaviour (no breaking change)

--all now also builds the PDF, but treats it as best-effort: if WeasyPrint isn't installed it warns and still returns 0 on the (successful) HTML, so existing report --all callers/CI without the pdf extra keep working. Only an explicit --pdf that cannot be honoured returns non-zero (you asked for a PDF and didn't get one). Locked by a test that mocks WeasyPrint away and asserts --all → 0, --pdf → 1.