feat(notes): service-layer support for notes on entry and month_entry

add_entry and add_month_entry accept an optional notes keyword. A
new set_entry_notes function updates a single budget entry's notes.
update_month_entry gains a notes parameter guarded by a sentinel so
callers can distinguish "do not touch notes" from "clear to NULL".
create_month copies entry.notes into each freshly snapshotted
month_entry. Blank / whitespace notes normalise to NULL.

Refs #13

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/quartermaster/month_service.py

@@ -112,6 +112,7 @@ def create_month(db: Session, year_month: str) -> Month:
             name=e.name,
             planned=e.amount,
             applied=Decimal("0.00"),
+            notes=e.notes,
             origin_name=e.name,
             origin_planned=e.amount,
             source_entry_id=e.id,
@@ -203,12 +204,20 @@ def section_view(month: Month, section: Section, label: str) -> MonthSectionView
     )
 
 
+def _clean_notes(raw: str | None) -> str | None:
+    if raw is None:
+        return None
+    stripped = raw.strip()
+    return stripped if stripped else None
+
+
 def add_month_entry(
     db: Session,
     month: Month,
     section: Section,
     name: str,
     planned: Decimal,
+    notes: str | None = None,
 ) -> MonthEntry:
     entry = MonthEntry(
         month_id=month.id,
@@ -216,6 +225,7 @@ def add_month_entry(
         name=name.strip(),
         planned=planned,
         applied=Decimal("0.00"),
+        notes=_clean_notes(notes),
         origin_name=None,
         origin_planned=None,
         source_entry_id=None,
@@ -243,6 +253,9 @@ def delete_month_entry(db: Session, month: Month, entry_id: int) -> Section | No
     return section
 
 
+_NOTES_SENTINEL = object()
+
+
 def update_month_entry(
     db: Session,
     month: Month,
@@ -251,6 +264,7 @@ def update_month_entry(
     name: str | None = None,
     planned: Decimal | None = None,
     applied: Decimal | None = None,
+    notes: str | None | object = _NOTES_SENTINEL,
 ) -> MonthEntry | None:
     entry = get_month_entry(db, month, entry_id)
     if entry is None:
@@ -261,6 +275,8 @@ def update_month_entry(
         entry.planned = planned
     if applied is not None:
         entry.applied = applied
+    if notes is not _NOTES_SENTINEL:
+        entry.notes = _clean_notes(notes)  # type: ignore[arg-type]
     db.commit()
     db.refresh(entry)
     return entry

src/quartermaster/service.py

@@ -87,14 +87,44 @@ def budget_zero(db: Session) -> Decimal:
     return (total_income - total_non_income).quantize(Decimal("0.01"))
 
 
-def add_entry(db: Session, section: Section, name: str, amount: Decimal) -> Entry:
-    entry = Entry(section=section, name=name.strip(), amount=amount)
+def add_entry(
+    db: Session,
+    section: Section,
+    name: str,
+    amount: Decimal,
+    notes: str | None = None,
+) -> Entry:
+    entry = Entry(
+        section=section,
+        name=name.strip(),
+        amount=amount,
+        notes=_clean_notes(notes),
+    )
     db.add(entry)
     db.commit()
     db.refresh(entry)
     return entry
 
 
+def _clean_notes(raw: str | None) -> str | None:
+    if raw is None:
+        return None
+    stripped = raw.strip()
+    return stripped if stripped else None
+
+
+def set_entry_notes(
+    db: Session, entry_id: int, notes: str | None
+) -> Entry | None:
+    entry = db.get(Entry, entry_id)
+    if entry is None:
+        return None
+    entry.notes = _clean_notes(notes)
+    db.commit()
+    db.refresh(entry)
+    return entry
+
+
 def delete_entry(db: Session, entry_id: int) -> Entry | None:
     entry = db.get(Entry, entry_id)
     if entry is None: