Story: Generate SVG support timelines with Node.js #126

Parent Epic: #125

As a documentation maintainer,
I want a Node.js function that generates an SVG timeline from roadmap data,
so that library release schedules are represented consistently and reproducibly.

Context

Follow the calendar structure of PHP's Supported Versions page: one row per branch, a shared time axis, colored periods, and a legend. Use LongitudeOne's site colors. Generate the SVG at build time without requiring daily updates.

Acceptance Criteria

• A function callable from Node.js returns a standalone SVG from library branch data and the global display window.
• Each branch has a labeled row; the time axis has annual graduations and period positions and lengths reflect their dates.
• Future releases, active support, and security-fixes-only periods are visually distinct and explained in a legend.
• Colors follow the site's palette; text and periods remain readable in light and dark themes.
• No relative duration or countdown appears.
• Missing or unannounced information never produces invented dates or periods; roadmaps without stable releases remain representable.
• Invalid dates and inconsistent period ordering produce diagnostics identifying the affected library and branch.
• The SVG includes an accessible title and description and scales without truncating information.
• Identical data and parameters produce identical output.
• Input supports one JSON file per library and a site-wide time-window configuration.
• Each branch has a version and an explicit planned or released status; passing a planned date never automatically changes that status.
• plannedReleaseDate is distinct from releaseDate; released branches require an actual release date.
• A future branch with a known planned date has a marker at that date; support periods are drawn only when announced.
• Release and support dates use YYYY-MM-DD; unknown values are null.
• Support end dates are explicitly configured, not derived from a fixed support duration; their chronological order is validated against the applicable release date.
• Timelines respect the common display bounds and indicate periods continuing beyond those bounds.

Constraints

• Use Node.js, compatible with the repository runtime requirements (Node.js 20+, with Node.js 24 in CI).
• Produce a standalone SVG image without MDX or client-side JavaScript required for display.
• Share the input contract with the integration Story so the table and timeline consume the same data.
• Do not implicitly apply PHP's support durations to LongitudeOne libraries.
• Roadmap configuration does not replace existing Packagist-based documentation version classification.

Definition of Done

The project's common Definition of Done applies.

• Document the input contract, parameters, errors, and a configuration example.
• Document library, branches, version, status, plannedReleaseDate, releaseDate, activeSupportUntil, securitySupportUntil, php, and notes, together with the global window bounds.
• Tests cover period placement, transitions, missing data, SVG escaping, invalid dates, and chronological validation.
• Representative SVGs are visually checked at small and large widths in both themes.
• npm test, npm run build, and applicable Markdown lint checks pass.
• Common composer test-local and composer quality checks apply only if defined in the repository; otherwise record them as not applicable to this Node.js project.