Add shared engineering rule contracts

- go-logging: slog, server-side only, structured attributes
- go-database: MySQL cursor safety, soft delete, GORM tags, fail-fast, N+1 prevention
- go-background-tasks: Task Manager pattern, polling, no SSE
- go-code-style: layering, error wrapping, startup sequence, config, templating
- import-export: CSV Excel-compatible rules (BOM, semicolon, decimal comma, DD.MM.YYYY)
- table-management: filtering and pagination rules added
- CLAUDE.template.md: updated to reference all shared contracts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

kit/patterns/table-management/contract.md

@@ -75,6 +75,30 @@ Canonical mapping:
   - right-aligned action icons.
 - Row action icons in `actions` column are intentionally smaller than toolbar icons.
 
+## Filtering Rules
+
+- Filters live above the table, in a dedicated filter bar or inline in the toolbar.
+- Every active filter must be visually indicated (highlighted field, chip, or badge count).
+- Applying a filter always resets pagination to page 1.
+- Filter state must be reflected in the URL as query parameters so the page is bookmarkable/shareable.
+- "Reset filters" clears all filter fields and reloads with no filter params.
+- Server-side filtering only — do not filter an already-loaded JS array client-side unless the full
+  dataset is guaranteed small (< 500 rows) and never grows.
+- Filter inputs debounce text input (300–500 ms) before triggering a server request.
+
+## Pagination Rules
+
+- Pagination is server-side. Never load all rows and paginate client-side.
+- URL query parameters carry page state: `?page=2&per_page=50`.
+  - `page` is 1-based.
+  - `per_page` defaults to a fixed project constant (e.g. 50); user may change it from a fixed set
+    (25 / 50 / 100).
+- The server response includes: `total_count`, `page`, `per_page`, `total_pages`.
+- Display: "Showing 51–100 of 342" — always show the range and total.
+- Prev/Next buttons are disabled (not hidden) at the boundary pages.
+- Direct page-number input is optional; if present it clamps to `[1, total_pages]` on blur.
+- Changing `per_page` resets to page 1.
+
 ## Reuse Rule
 
 If a pattern needs table selection + bulk actions, it must: