feat(backend+frontend): add is_regex support to dictionary entries

Add support for regex-based dictionary entries across the full stack:

Backend:
- DictionaryEntry model: add is_regex column (Boolean, default False)
- DictionaryEntryCRUD: validate regex on add_entry(), compile on creation
- _enforce_dictionary: match by regex pattern when is_regex=True
- dictionary_filter: support is_regex in filter/query
- metrics: include is_regex entries in metrics calculations
- Alembic migration: 20260604_add_is_regex_to_dictionary_entries
- Merge migration: 351afb8f961a (merge is_regex + composite index heads)

Frontend:
- DictionaryDetailModel: add is_regex field to DictionaryEntry interface,
  EditForm, and addForm; sync edit/add form state with backend schema

backend/src/models/translate.py

@@ -142,8 +142,7 @@ class TranslationRecord(Base):
     __table_args__ = (
         Index("ix_translation_records_run_status", "run_id", "status"),
         Index("ix_translation_records_source_hash_status", "source_hash", "status"),
-        Index("ix_translation_records_run_source_hash", "run_id", "source_hash",
-              comment="Composite index for NOT EXISTS dedup subquery"),
+        Index("ix_translation_records_run_source_hash", "run_id", "source_hash"),
     )
 # #endregion TranslationRecord
 
@@ -230,6 +229,7 @@ class DictionaryEntry(Base):
     context_data = Column(JSON, nullable=True, comment="Structured context for term usage")
     usage_notes = Column(Text, nullable=True, comment="Usage guidance for the term mapping")
     has_context = Column(Boolean, default=False, comment="Whether context_data is populated")
+    is_regex = Column(Boolean, default=False, comment="Whether source_term is a regex pattern")
     context_source = Column(String, nullable=True, comment="auto|auto_with_edits|manual|bulk")
     origin_source_language = Column(String, nullable=True, comment="Original source language of the term")
     origin_run_id = Column(String, nullable=True, comment="Run ID from which this correction originated")