refactor: prefix every table with its module

Two tables were named after the concept they came from rather than the module
they belong to, so the schema read as if the template tables were part of the
paper module. Renamed (data preserved, `RENAME TABLE` moves rows in place):

    paper_template  -> template                 the 模板 module
    section_field   -> template_field_library   the 字段库 the 模板 module owns

The paper tables and `template_field` already followed the rule. The rename
carries through everything that named a module:

  models   Template, TemplateField, TemplateFieldLibrary
  schemas  Template*, TemplateFieldLibrary*
  crud     app/crud/template.py, app/crud/template_field_library.py
  API      /template-field-library (was /section-fields); handlers are now
           named after library entries, which removes the ambiguity with
           TemplateField — a placement, a different thing entirely
  client   src/api/templateFieldLibrary.ts

`paper_template_filed_sort` is deliberately untouched: it is a column of the
paper module, spelled as the feature was specified.

TiDB v8.5 with tidb_enable_foreign_key on — as this cluster runs — enforces
foreign keys rather than ignoring them, so the docs' "TiDB does not enforce
foreign keys" was wrong. Corrected, with what actually follows from it: the
rename was rehearsed (RENAME TABLE carries a referencing constraint along), the
API keeps checking first so a violation names the row instead of surfacing a
driver error, and the ORM cascades stay so behaviour does not depend on a
cluster setting.

Revision f27a1c6d9e04 verified both ways; 40 smoke checks, type-check and build
all pass.

backend/app/schemas/template.py

@@ -0,0 +1,123 @@
+"""Request/response schemas for templates (模板管理)."""
+
+from datetime import datetime
+from decimal import Decimal
+
+from pydantic import BaseModel, ConfigDict, Field
+
+from app.models.template import Template
+from app.models.template_field import TemplateField
+from app.schemas.common import TypographyMixin
+
+
+class TemplateFieldInput(BaseModel):
+    """One placement of a library field inside a template.
+
+    The client sends the whole ordered selection on create and on update; the
+    server replaces the stored rows with it. ``sort`` is a plain ascending
+    integer and is the *only* thing that decides render order.
+    """
+
+    field_id: int
+    sort: int = Field(default=0, ge=-1_000_000, le=1_000_000)
+
+
+class TemplateFieldRead(TypographyMixin, BaseModel):
+    """A template's field, flattened with the library row it points at.
+
+    Persistence keeps the two apart — a placement row plus the library row it
+    references — but a client rendering an outline wants one flat record, so
+    the typography is denormalised into the response. That is also what keeps
+    the outline in sync: there is only ever one copy of a field's name and
+    styling, in the library.
+    """
+
+    id: int
+    field_id: int
+    sort: int
+    name: str
+    level: int
+    font_size: Decimal
+    font_color: str
+
+    @classmethod
+    def from_model(cls, item: TemplateField) -> "TemplateFieldRead":
+        """Flatten a placement row and its library row into one record."""
+        return cls(
+            id=item.id,
+            field_id=item.field_id,
+            sort=item.sort,
+            name=item.field.name,
+            level=item.field.level,
+            font_size=item.field.font_size,
+            font_color=item.field.font_color,
+        )
+
+
+class TemplateBase(BaseModel):
+    """Shared body of the create/update payloads."""
+
+    name: str = Field(min_length=1, max_length=255)
+    abstract: str | None = None
+
+
+class TemplateCreate(TemplateBase):
+    """Payload for ``POST /templates``.
+
+    The field selection is free: any subset, any order, repeats allowed. The
+    server stores it as given and orders it by ``sort`` on read.
+    """
+
+    fields: list[TemplateFieldInput] = Field(default_factory=list)
+
+
+class TemplateUpdate(BaseModel):
+    """Payload for ``PATCH /templates/{id}``.
+
+    ``fields`` is a full replacement when present — omit it to leave the
+    selection untouched.
+    """
+
+    name: str | None = Field(default=None, min_length=1, max_length=255)
+    abstract: str | None = None
+    fields: list[TemplateFieldInput] | None = None
+
+
+class TemplateListItem(BaseModel):
+    """A template as it appears in the list table — no field rows."""
+
+    model_config = ConfigDict(from_attributes=True)
+
+    id: int
+    name: str
+    abstract: str | None
+    field_count: int
+    created_at: datetime
+    updated_at: datetime
+
+
+class TemplateRead(BaseModel):
+    """A template with its outline, already ordered by ``sort``."""
+
+    model_config = ConfigDict(from_attributes=True)
+
+    id: int
+    name: str
+    abstract: str | None
+    #: The outline, ordered by ``sort`` — the ORM relationship sets that
+    #: ordering, so this list is display-ready with no client-side sorting.
+    fields: list[TemplateFieldRead]
+    created_at: datetime
+    updated_at: datetime
+
+    @classmethod
+    def from_model(cls, template: Template) -> "TemplateRead":
+        """Build the response from a template and its placement rows."""
+        return cls(
+            id=template.id,
+            name=template.name,
+            abstract=template.abstract,
+            fields=[TemplateFieldRead.from_model(item) for item in template.items],
+            created_at=template.created_at,
+            updated_at=template.updated_at,
+        )