Rename rawPath to contentPath, add dataPath, support series abstract …

[noha]

…override

Part of a broader site-layout rework Norbert wants (content/ vs data/ vs static/, discussed in chat): content/ is everything that lands in the target dir (processed or verbatim-copied), data/ is files Foliage needs while building that never become their own published page. static/ is deliberately NOT part of this change - still under discussion, not decided yet.

• FOWebSite: rawPath/rawPath:/defaultRawPath/relativeRawPath: renamed to contentPath/contentPath:/defaultContentPath/relativeContentPath: (default 'content' instead of 'raw'). New dataPath/dataPath:/defaultDataPath (default 'data'), same ivar-with-overridable-default shape as the other paths.
• FOPublisher: gained a matching dataPath/dataPath: (default 'data'), nested under sourcePath the same way templatePath already is; passes both through in publish.
• FOImporter/FOWebResource: updated to the renamed API (relativeContentPath:, comment wording).
• FOSeries>>abstract: now checks data/series/.md first (frontmatter
  • body, read directly from disk via FOFrontmatterParser/FOMarkdownParser
  • deliberately NOT through FOImporter/the site tree, since a page at that exact slug would collide with the auto-generated series overview page) and falls back to the first post's own abstract when no such file exists. Body only, no frontmatter fields read from it yet (e.g. a title override) - not asked for, matches the file's whole purpose today (a hand-written abstract, nothing else).

Verified: full suite green (Foliage-Core-Tests, Foliage-Publisher-Tests, Foliage-Markdown-Tests, Foliage-Frontmatter-Tests), plus a real dry run against noha.github.io's renamed content/ tree (companion change in that repo) - import + full publish, including series pages, completes with no errors and the same output as before the rename.