Add attachments to service, maintenance, fuel and parts records

Documents already carried a single optional file: upload, download, detach,
access-checked on every request and proxied through this server, so PocketBase's
files are never public URLs. Service records, workshop visits, refills and
catalog parts all want the same thing — a receipt, an invoice, a photo of the
box — so extend it to them.

Rather than copy the document handlers four more times, lift them into one
shared layer. Every attachable collection has a car relation and a file field,
which is what lets a single set of handlers authorize and serve all of them. An
upload finishes by delegating to the collection's own GET handler, so the
response carries the full record — derived fields and all — exactly as a re-read
would. The web side gets the same treatment: one picker component and one
upload-after-save helper behind all five forms. Net effect is five features for
about the cost of the one that was already there.

Alongside:
- parts gain a notes field
- Reminders moves behind Parts catalog in the car detail tabs
- the changed-part labels spell out in full ("Oil & Oil filter" rather than
  "Oil & filter"), and the form and table now agree

The PocketBase schema must be migrated before the new attachments work:
scripts/setup-pocketbase.mjs adds the file fields and parts.notes. It is
additive and safe to re-run.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

API Server/internal/models/models.go

@@ -10,6 +10,18 @@ package models
 
 import "time"
 
+// Attachment is the single optional file a record carries — a scan, a receipt, a
+// workshop invoice, a photo of a part's box. Embedded by every type that can
+// hold one.
+//
+// FileName is the name PocketBase stored it under. The bytes are not in here:
+// they are served from GET /api/{records}/{id}/file, which re-checks access on
+// every request, so an attachment is never a public URL.
+type Attachment struct {
+	FileName string `json:"fileName,omitempty"`
+	HasFile  bool   `json:"hasFile"`
+}
+
 // Car corresponds to one worksheet in the original spreadsheet.
 type Car struct {
 	ID           string `json:"id"`
@@ -64,6 +76,9 @@ type ServiceRecord struct {
 
 	Notes string `json:"notes,omitempty"`
 
+	// The workshop receipt or stamped service-book page for this visit.
+	Attachment
+
 	// Derived (not stored): filled in by the API on read.
 	NextServiceDate *time.Time `json:"nextServiceDate,omitempty"` // Excel col C
 	NextServiceKm   *int       `json:"nextServiceKm,omitempty"`   // Excel col D
@@ -79,6 +94,10 @@ type Part struct {
 	Name       string `json:"name"`       // e.g. "Oil Filter"
 	PartNumber string `json:"partNumber"` // e.g. "04152-YZZA7"
 	Category   string `json:"category"`   // optional: oil|filter|wiper|other
+	Notes      string `json:"notes,omitempty"`
+
+	// A photo of the box, or the spec sheet for the part.
+	Attachment
 
 	Created string `json:"created,omitempty"`
 	Updated string `json:"updated,omitempty"`
@@ -112,6 +131,9 @@ type FuelEntry struct {
 	Station string `json:"station,omitempty"`
 	Notes   string `json:"notes,omitempty"`
 
+	// The pump receipt.
+	Attachment
+
 	// Derived (not stored): filled in by the API on read.
 	PricePerLiter   *float64 `json:"pricePerLiter,omitempty"`
 	DistanceKm      *int     `json:"distanceKm,omitempty"`      // since the previous full tank
@@ -169,6 +191,9 @@ type MaintenanceEntry struct {
 	WarrantyUntil *time.Time `json:"warrantyUntil,omitempty"`
 	Notes         string     `json:"notes,omitempty"`
 
+	// The workshop's invoice.
+	Attachment
+
 	// Derived (not stored): filled in by the API on read.
 	TotalCost        float64 `json:"totalCost"`
 	WarrantyActive   *bool   `json:"warrantyActive,omitempty"`
@@ -196,10 +221,8 @@ type CarDocument struct {
 	Cost       float64    `json:"cost"`
 	Notes      string     `json:"notes,omitempty"`
 
-	// FileName is the stored attachment (scan/PDF), served via
-	// GET /api/car-documents/{id}/file. Empty when nothing is attached.
-	FileName string `json:"fileName,omitempty"`
-	HasFile  bool   `json:"hasFile"`
+	// The scan or photo of the paperwork itself.
+	Attachment
 
 	// Derived (not stored): filled in by the API on read.
 	Expiry ExpiryAssessment `json:"expiry"`