[FEAT] Add the OVIDE MOC-intensity reader, plus a y-axis label-wrap helper

[eleanorfrajka]

Summary

Adds OVIDE as a new array: the monthly MOC-intensity time series across the Greenland-Portugal A25 OVIDE line (Mercier et al., SEANOE 10.17882/46445), a satellite-altimetry-plus-Argo estimate. Also adds a small plotting helper that wraps long variable labels so they fit a plot y-axis.

OVIDE reader

• New array ovide, served through read.ovide() (a blended/estimated product). Source is a single SEANOE netCDF (46195.nc), licence CC-BY-NC-4.0. Reader modelled on the existing single-file altimetry readers.
• The file provides two MOC indices on different monthly time axes: an in-situ index over 2002-2015 (AVISO surface velocities combined with the time-varying Argo/ISAS interior) and an altimetry proxy over 1993-2015 (AVISO combined with a fixed 2002-2015 mean Argo/ISAS interior), plus the in-situ ensemble standard deviation. Their monthly timestamps coincide exactly, so the reader reindexes them onto a single 1993-2015 TIME axis (the in-situ series is NaN before 2002) rather than carrying two time coordinates.
• Served variables: MOC_SIGMA1 (in-situ index), MOC_SIGMA1_PROXY (altimetry proxy), MOC_SIGMA1_ERR (ensemble standard deviation). The MOC index is the maximum of the overturning streamfunction in sigma1 space (potential density referenced to 1000 dbar), so MOC_SIGMA1/MOC_SIGMA1_PROXY carry standard_name: ocean_meridional_overturning_streamfunction with cell_methods: "SIGMA1: maximum" and reference_pressure: 1000; the uncertainty carries no standard_name.
• Metadata in metadata/ovide.yml (title, citation, licence, weblink, contributors, institution) passes array_schema.json. Attribution is verified, not guessed: the three author ORCIDs were confirmed against the ORCID API and added to contributor_registry.yml, and the institution (Laboratoire d'Oceanographie Physique et Spatiale, LOPS) with EDMO code 4536 was added to institution_registry.yml.
• Wired into data_sources/__init__.py, read.py (read.ovide, SUPPORTED_STANDARDIZATION, __all__), and defaults.py (ARRAY_NAMES + description). Tests in tests/test_ovide.py (fast registration + schema checks; a slow integration test of the two-index merge).
• README array table updated.

Plot label wrapping

• Adds plotters._vlabel(label, width=24), which word-wraps a long axis label onto multiple lines at word boundaries (short names are returned unchanged). Wired into plot_amoc_timeseries, which the report timeseries plots route through, so long standardised long_name labels no longer overflow the y-axis. The docstring notes it can later grow into a registry-based name translator.

Verification

429 fast tests pass; the slow OVIDE integration test passes against the downloaded file; ruff and ruff-format clean.

Breaking changes and migration

None. OVIDE is a new array (additive); _vlabel is an internal plotting helper.