Re-vendor carve-lib + block-attribute corpus + grammar precision

[dereuromark]

Completes the block-attribute-line rollout on the carve side (PART 9 §15, spec #25; carve-js carve-js#22; carve-php already conformant).

• carve-lib re-vendored from carve-js main (block-attr parser + per-block-type attr rendering).
• examples.md + corpus — three new Attributes fixtures: 17-attributes-2 (single attr line → paragraph), -3 (consecutive class accumulation), -4 (attrs on a list). All class-focused so they agree byte-for-byte across carve-js AND carve-php (verified); they deliberately avoid the separate multi-attribute render-order divergence (carve-js class id key vs carve-php id class key), tracked separately.
• grammar.ebnf — tightens block_attributes to match both reference impls: a continuation is a single line break (+indent), and a blank line inside the braces ends the block (not interior padding). The earlier ws_nl form over-claimed blank-line support neither impl provides. Adds §15 notes on the blank-line and quoted-}-across-lines (pathological) edges.

93/93 corpus + normativity pass.

Codex flagged that a {...} line after paragraph text (no blank) doesn't attach to the following block. Verified false positive: neither djot-php nor carve-php attaches it either — both drop it. Making {...} a paragraph-breaker would make carve-js diverge from the reference on Para\n{.note}\nNext (which the reference joins into one paragraph). The §15 feature targets leading attribute lines; the mid-prose case matches the reference in dropping the attr.