Fix Hebrew text rendering inconsistency (#20336)

[veerababu1729]

Problem

Hebrew text "אישור אגודה לחתימת" renders differently across PDF pages:

• ✅ Correct on pages with more Hebrew
• ❌ Reversed on pages with mostly English

Solution

Enhanced bidi.js algorithm to detect pure Hebrew content and handle it consistently.

Changes

• src/core/bidi.js: Improved base direction detection (lines 167-209)
• test/unit/bidi_spec.js: Added Hebrew consistency tests (lines 72-106)

Results

Fixes #20336

• ✅ Hebrew text now consistent across all contexts
• ✅ All existing tests still pass
• ✅ Fixes search/copy-paste issues with Hebrew PDFs

Test Evidence

// Before: Inconsistent
"Document אישור אגודה לחתימת file" → RTL ✅
"Long English text אישור אגודה לחתימת more" → LTR (Hebrew reversed) ❌

// After: Consistent  
"Document אישור אגודה לחתימת file" → RTL ✅
"Long English text אישור אגודה לחתימת more" → LTR (Hebrew correct) ✅


**Key Points:**
- 🎯 **Clear problem**: Hebrew text inconsistency
- 🔧 **Simple solution**: Better detection algorithm  
- 📊 **Proof**: Before/after examples
- ✅ **Safe**: No breaking changes
- 🧪 **Tested**: New tests + existing tests pass

[veerababu1729]

Please let me know anything