mermaid-text-0.28.2

Fixed — B-title: vertical routes overwrote subgraph title characters with

junction glyphs

Root cause: draw_subgraph_border calls seed_border_dirs on every cell of
the subgraph's top border row (including the cells that will hold the inline
label) to enable proper junction rendering where routes cross the border.
write_text_protected then stamps the label and marks those cells protected.
However, Grid::add_dirs only honours protection when directions == 0. The
seeded DIR_LEFT | DIR_RIGHT bits remained on the label cells, so when edge
routing called add_dirs through a title cell, the protection flag was bypassed
and the label character was replaced with a junction glyph (┼, ┬, etc.).
Example: "Backend" rendered as Backen┼─┼.

Fix (Option A — guard on grid direction bits):

New Grid::clear_dirs method (1 function, ~10 lines) that zeroes the direction
bits of a cell without touching its glyph or protection flag. Called in
draw_subgraph_border after write_text_protected for each label cell. With
directions set back to 0, add_dirs correctly skips the protected label cell and
the title is preserved.

Diff classification:

• 2 Improvement (A): flowchart_subgraphs_tb (natural + width80) — "Backend"
  title is now intact.
• 0 Neutral (B)
• 0 Regressions

New regression test: route_does_not_pierce_subgraph_title_row.
B9 / B12 / B3 / width-budget fixes unaffected.