fix(utils): bound Mermaid ASCII pathfinder

[roboomp]

Repro

The provided four-node Mermaid flowchart reproduced the hang with timeout 5s bun .wt/repro-mermaid-ascii.ts: before the fix the harness produced no output and exited 124, showing renderMermaidAsciiSafe() did not return within the bounded run.

Cause

packages/utils/src/vendor/mermaid-ascii/ascii/pathfinder.ts#getPath searched every free coordinate in the non-negative quadrant and only returned null after the priority queue emptied. When packages/utils/src/vendor/mermaid-ascii/ascii/edge-routing.ts#determinePath asked for an unreachable attachment point, the queue could never exhaust, so the existing direct fallback path was never reached.

Fix

• Added occupied-grid/search-endpoint bounds with a routing margin around getPath().
• Added an expansion budget backstop so pathological routes return null instead of growing unbounded state.
• Added regression coverage for the reported declaration-order graph and an enclosed destination attachment point.
• Added a utils changelog entry for the renderer termination fix.

Verification

Ran timeout 5s bun .wt/repro-mermaid-ascii.ts after the fix; it returned in about 8 ms with output length 419. Ran bun test packages/utils/test/mermaid-ascii.test.ts with 3 passing tests. Ran bun run check in packages/utils successfully. Fixes #5293