docs: correct stale toolchain version and unwrap prose

[Chemaclass]

🔗 Ticket

🤔 Background

Two real defects surfaced while auditing the docs after #64:

• CONTRIBUTING.md still pinned bashunit 0.17.0 in the toolchain table. The repo moved to 0.45.0 in chore(deps): update bashunit to 0.45.0, pin CI actions, add --jobs #64, so a contributor matching that table would install a version whose doubles API the suite no longer targets — exactly the failure chore(deps): update bashunit to 0.45.0, pin CI actions, add --jobs #64 was about.
• The landing page advertised concurrency as BASHDEP_JOBS only, predating the --jobs=N flag.

Separately, all prose was hard-wrapped at 80 columns, which makes documentation diffs noisy: rewording one sentence reflows the entire paragraph.

💡 Goal

Make the docs accurate against the current code, and stop hard-wrapping markdown prose.

🔖 Changes

• CONTRIBUTING.md: bashunit 0.17.0 → 0.45.0 in the toolchain table.
• site/index.html: the feature list, the feature card, and the pipeline diagram now name --jobs=N alongside BASHDEP_JOBS. Diagram column alignment preserved.
• Unwrapped prose in README.md, docs/api.md, docs/behavior.md, docs/README.md, docs/releasing.md, .github/CONTRIBUTING.md.

The unwrap was scripted with code fences, tables, blockquotes, headings, indented blocks and list-item boundaries all protected, then diff-reviewed. Only prose lines were joined — no wording changed, nothing reordered, no content removed.

🖼️ Screenshots

BEFORE

- `bashdep::clean` returns the number of orphans it could not remove
  (capped at 255), reporting each failed removal to stderr; `0` when all
  orphans were removed.

AFTER

- `bashdep::clean` returns the number of orphans it could not remove (capped at 255), reporting each failed removal to stderr; `0` when all orphans were removed.

✅ Verification

• make check clean: 252 tests, ShellCheck, editorconfig
• .editorconfig sets max_line_length for **.sh (120) only, never for **.md, so the long lines lint clean
• Tables, code blocks and multi-line bullets spot-checked in every touched file