style: adopt golangci-lint v2 and resolve all findings

Add .golangci.yml (v2): the standard linters plus bodyclose, errorlint, noctx, misspell, rowserrcheck, sqlclosecheck, unconvert, usestdlibvars, with gofumpt + goimports formatters. Enable the std-error-handling exclusion preset for idiomatic Close/Remove/Setenv ignores; scope-exclude SA1019 (parser.ParseDir in tools/openapigen) and ST1005 (intentional capitalized user-facing error copy that tests assert verbatim). No inline nolint directives were introduced.

Resolve all 217 findings behavior-preserving: gofumpt/goimports formatting, explicit blank assignment on intentionally ignored errors, errors.Is/errors.As and %w wrapping, context-aware stdlib calls (CommandContext/QueryContext/NewRequestWithContext/Dialer), staticcheck simplifications, removed redundant conversions, http.StatusOK and http.MethodGet, inlined the go:fix intPtr helper, and deferred sql rows Close. Add a golangci CI job mirroring the existing Go jobs.

internal/web/network/auto_https_conn.go

@@ -50,7 +50,7 @@ func (c *AutoHttpsConn) readRequest() bool {
 	resp.StatusCode = http.StatusTemporaryRedirect
 	location := fmt.Sprintf("https://%v%v", request.Host, request.RequestURI)
 	resp.Header.Set("Location", location)
-	resp.Write(c.Conn)
+	_ = resp.Write(c.Conn)
 	c.Close()
 	c.firstBuf = nil
 	return true